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 THE UNIVERSITY 
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 OF THE 
 
 UNIVERSITY OF ILLINOIS 
 
 WON CIRCULATING 
 
UNIVERSITY OF ILLINOIS 
 Agricultural Experiment Station 
 
 BULLETIN No. 178 
 
 RECENT ILLINOIS WORK ON THE CORN 
 
 ROOT-APHIS AND THE CONTROL 
 
 OF ITS INJURIES 
 
 BY STEPHEN A. FORBES 
 STATE ENTOMOLOGIST 
 
 URBANA, ILLINOIS, JANUARY, 1915 
 
RECENT ILLINOIS WORK ON THE CORN 
 
 ROOT-APHIS AND THE CONTROL 
 
 OF ITS INJURIES 
 
 BY STEPHEN A. FORBES, STATE ENTOMOLOGIST 
 
 The corn root-aphis, or corn root-louse, as it is more commonly 
 called, is now the most generally injurious insect pest of the corn field 
 in Illinois. Its injuries have been but little checked by all that has been 
 done and printed concerning it, and they are evidently increasing slow- 
 ly in total effect. There is, in fact, no other corn-field insect which is 
 so frequently called to the attention of the economic entomologist. 
 Nevertheless, the corn-root-aphis problem has been practically solved 
 not, perhaps, in the best way possible, or as completely as will be the 
 case when time, money, and skilled assistance are all available for fur- 
 ther studies and experiments. Undoubtedly, however, if the results 
 which have already been established were generally put to use in the 
 practice of the Illinois farmer, this aphis would presently lose its place 
 at the head of the list of insects affecting corn, and would be classed 
 among those which are only occasionally injurious enough to call for 
 special notice. 
 
 It is the purpose of this article to set forth the results of our more 
 recent investigations and experiments (1907-1910) in all necessary de- 
 tail, and to show what they signify and how they apply to the routine 
 of corn culture in this state. 
 
 The key to the control of this insect is to be found in its spring 
 condition in old corn fields which have been infested by it the year 
 preceding ; and in the fact that corn is the only crop-plant upon which 
 it lives and multiplies. This is substantially shown by the following 
 facts. 
 
 1. The eggs left by the corn root-lice in fall when the insects 
 themselves perish, are virtually all in the earth in corn fields. They 
 are collected there by the corn-field ant, which keeps them in its un- 
 derground burrows until they hatch the following April and May. 
 
 2. As the young root-lice escape from the egg they are placed by 
 these ants on the roots of pigeon-grass, smartweed, and other corn- 
 field weeds, on which they live by sucking the sap, giving off at the 
 same time an abundant fluid excrement which is lapped up by the 
 ants as food. 
 
 3. The root-lice hatching from the egg are all females, and pro- 
 duce no eggs, but bring forth living young when they themselves are 
 
406 BULLETIN No. 178 [January, 
 
 about two weeks old. Their young, in turn, reproduce in the same 
 way, one generation succeeding another at shorter intervals as the 
 weather warms up, until in midsummer they are only a week apart. 
 The average number of complete generations for the season is about 
 sixteen in the latitude of central Illinois. 
 
 4. The second generation of this series begins to appear in cen- 
 tral Illinois about the first of May, and the oldest of these will begin 
 to give birth to the third generation on or before the middle of that 
 month. So rapid is the rate of reproduction that by the end of June 
 as many as six generations may have made their appearance. 
 
 5. The root-lice of the first generation those hatching from the 
 egg are all wingless ; but beginning with the second generation a vari- 
 able percentage of this and of all following generations may acquire 
 wings. These winged root-lice, called migrants, may thus begin to 
 appear early in May. 
 
 6. By means of these winged insects originating in old corn 
 ground, fields not infested the year before may become infested from 
 the first week in May onward. Root-aphis injury is thus like a con- 
 tagious disease, spreading from field to field on the wings of the es- 
 caping migrants. As these fall to the ground they are taken in charge 
 by the corn-field ant, which carries them under ground and places 
 them on the roots of plants, where they begin to feed and to bring 
 forth living young precisely as do the wingless ones. The young born 
 from winged mothers are wingless or winged, according to circum- 
 stances, just as are those whose mothers are themselves without wings. 
 
 7. As the winged lice may begin to come up out of the ground 
 and fly away even before corn is planted for the new crop, and will 
 continue to do so thruout the season, fields that were not in corn 
 the year before may become infested by these winged migrants and 
 their young while the corn is still very small. 
 
 8. The corn-field ant is indispensable to the root-lice, which it 
 carries about from place to place as may be necessary, transferring 
 them to the roots of fresh plants when those they have been feeding 
 upon become sapped or overcrowded. 
 
 9. If an old infested corn field is planted to some other crop than 
 corn, the root-lice living in it feed on the weeds until these are smoth- 
 ered out by the new crop-plants. Many of them then acquire wings 
 and fly away, and others are eaten by the ants which have them in 
 charge. The field is in this way virtually cleared of them ; but the sur- 
 vivors are widely dispersed, to infest other fields. 
 
 10. If an old infested corn field is planted to corn, the lice, placed 
 at first on the roots of the corn-field weeds, are transferred by the 
 
<'9/5J CORN ROOT-APHIS AND CONTROL OF ITS INJURIES 407 
 
 ants to the roots of the corn plants as the weeds in the field are de- 
 stroyed by cultivation,, and there they continue to multiply the whole 
 season thru. 
 
 11. The corn root-louse may live and propagate thru the sea- 
 son on a considerable variety of other plants, including several com- 
 mon weeds, but on none of them in numbers to make the fact a matter 
 of serious economic importance. Injury to corn by root-lice is almost 
 wholly due to those which have fed and bred in fields of corn, and not 
 to the. comparatively scanty stock which lives on other plants. From 
 this it appears that if they are generally prevented from getting a start 
 in corn fields in spring, their injury to corn will be insignificant. 
 
 12. The root-lice may be most easily destroyed in early spring, 
 and a strong check may also be put upon the multiplication of the 
 corn-field ants by early plowing of old corn fields to a depth of six or 
 seven inches, followed by repeated deep disking as a preparation of the 
 ground for corn. This treatment acts by killing and keeping down 
 the young weeds on which the root-lice are feeding, and by breaking 
 up the burrows of the ants and scattering the eggs and young of the 
 root-lice and the eggs and young of the ants themselves thru the dirt 
 so thoroly that the ants can not recover their. property even if they 
 remake their nests. 
 
 13. As corn planted on ground not in that crop the year before 
 may become infested by winged root-lice from neglected fields of last 
 year's corn, anything like a general control of the injury requires a 
 general clearing up of old infested fields in spring. So far as possible, 
 any such fields should be treated as prescribed under No. 12, both as 
 a protection, of one's own corn crop, which is likely to be first and 
 most heavily infested, as a rule, by the root-lice of one's own raising, 
 and also as a duty to one's neighbors, whose crops should not be left 
 to suffer injury because of one's own negligence. 
 
 14. When this program of preventive preparation of old corn 
 fields can not be fully carried out, some temporary advantage may 
 sometimes be gained in the beginning by planting with the seed sub- 
 stances so offensive and repellent to the ants that they will keep out 
 of the hill until these have disappeared. Such substances are oil of 
 tansy, tincture of asafetida, oil of sassafras, anise oil, kerosene, oil of 
 lemon, and a number of other volatile oils and strong-smelling sub- 
 stances, the vapors from which the corn-field ants can not endure. 
 These fluids were formerly used by mixing the seed with them direct, 
 
8 BULLETIN No. 178 [January, 
 
 ut applied in this way they are likely, under certain weather condi- 
 .ions, to be injurious to the kernel and to the young plant. 1 
 
 15. While there is no evidence that the corn root-aphis thrives 
 best on comparatively unthrifty plants, as do many other insects, it is 
 sure that the corn plant endures the drain of its infestation with less 
 injury when the soil is fertile and the corn well cared for. The good 
 corn-farmer on a good corn-farm will consequently suffer less from 
 this insect, as a rule, than his less careful and less fortunate neighbor. 
 
 16. A frequent rotation of crops, with a short period in corn, is 
 a most valuable measure of prevention against root-louse injury, since 
 corn following some other crop than corn can only become infested 
 by means of root-lice coming into it from outside fields. 
 
 17. The more generally correct practices are followed in any 
 neighborhood the less will be the injury done by the root-aphis to 
 the fields even of those who pay no attention to it. On the other hand, 
 a general neglect of it will give it such opportunities of multiplication 
 that it will swarm out of infested fields in numbers to give its attacks 
 the character of an epidemic. It is consequently to the interest of 
 every one to do his best to establish the correct routine of corn culture 
 thruout his neighborhood, as well as to follow it carefully himself. 
 
 18. Finally, to prevent mistakes, the fact should be known that a 
 few other kinds of root-lice are likely to infest the roots of corn tem- 
 porarily, even when the crop is planted on ground not in corn the year 
 before. Certain grass root-lice and clover root-lice may live for a time 
 on corn, and may even do some injury in early spring, leaving the 
 fields, however, before the summer is over. 
 
 RECENT ARTICLES IN THE OFFICE REPORTS 
 
 My latest articles on the corn root-aphis, giving the results of ex- 
 periments in detail, were published in 1908 and 1909 in my Thirteenth 
 and Fourteenth reports. The first of these articles gives an account 
 of several field experiments made in 1904 and 1905, with deep plowing 
 and repeated disking of infested fields as a preparation of the ground 
 for planting; and the second article describes a long series of experi- 
 ments made in 1905 and 1906, in the insectary and in the field, with 
 various repellent substances applied to the seed at planting with a 
 view to excluding the ants and the root-lice from the hills. 
 
 statement concerning conditions under which seed-corn may be injured 
 by kerosene and other oils is based upon extensive and very careful experi- 
 ments made by Dr. J. H. Whitten when he was a graduate student in botany 
 at the University of Illinois. The results of these experiments have now been 
 published by him in detail in the Bulletin of the Illinois State Laboratory of 
 Natural History, Volume X, Article V. 
 
/o/5] CORN ROOT- APHIS AND CONTROL OF ITS INJURIES 409 
 
 In the first article 1 it was shown that after the usual plowing and 
 harrowing as a preparation for corn, disking three times additional 
 and harrowing once had the effect to reduce the number of root-lice 
 on the experimental plots 92 per cent, and the number of hills in- 
 fested by root-lice 82 per cent; and to reduce the number of ants 92 
 per cent and the number of hills infested by ants 64 per cent. It was 
 further shown that twice disking reduced the number of root-lice 84 
 per cent and the number of hills infested by them 75 per cent, the num- 
 ber of ants 65 per cent and the number of hills infested by them 59 
 per cent ; and that once disking reduced the root-lice and hills infested 
 by them 43 per cent and 41 per cent, and the ants and hills infested by 
 them 42 per cent and 33 per cent, respectively. All these ratios were 
 determined in each case by comparison with check plots in the same 
 fields which had received only the usual preparation for corn. 
 
 These facts, taken by themselves, seem thoroly conclusive and 
 highly satisfactory. Nevertheless, since corn root-lice, like most in- 
 jurious insects, are largely affected by the varying conditions of 
 weather, soil, and crop, it was thought necessary to test these conclu- 
 sions by repeating and varying the above experiments in a way to ar- 
 rive at maximum, minimum, and average benefits under the varying 
 phases and practices of Illinois agriculture. It is a part of the purpose 
 of this article to give the product of these later experimental studies 
 in detail. 
 
 The second article above referred to, 2 that published in my Four- 
 teenth Report, dealt especially with the effects of the treatment of seed- 
 corn with oil of lemon, carbolic acid, formalin, and pure kerosene, 
 with the general result that under the conditions of 1906, where seed- 
 corn was treated with oil of lemon just before planting in infested 
 fields, the yield was increased by 1,159 ear-bearing stalks to the acre, 
 while a similar treatment of the seed with carbolic acid increased the 
 yield by 945 such stalks, a formalin treatment by 742, and a kerosene 
 treatment by 274. 3 
 
 Notwithstanding this surprisingly favorable result, there was some 
 appearance of injury to the seed by all these substances. The check- 
 plot contained more living hills to the 80-rod row than any of the ex- 
 perimental plots, the difference being small, however, except in the 
 
 1 Field Experiments on the Corn Root-aphis (Aphis maidiradicis Forbes). 
 24th Rep. State Ent. 111., pp. 8-29. See especially the table on p. 29. 
 
 'Experiments with Repellents against the Corn Root-aphis, 1905 and 1906. 
 25th Rep. State Ent. 111., pp. 1-26. 
 
 3 25th Rep. State Ent. 111., p. 21. 
 
410 BULLETIN No. 178 [January, 
 
 plot treated with kerosene, the hills in which numbered only 82.5 per 
 cent of those in the check. 
 
 The whole operation of this year was regarded as provisional 
 only, and, in the language of my report, its conclusions were "taken as 
 applying exactly only to similar, if not identical, conditions a similar 
 soil similarly prepared, equally infested with the corn root-aphis, and 
 subject to similar weather conditions and with a treatment of seed 
 identical with ours in all particulars, including materials of the same 
 quality and strength. How far the results here described may be ex- 
 pected to apply to a different soil, less heavily, or even much more 
 heavily, infested, more thoroly prepared, and planted during either 
 a very wet spring or a very dry one, with a less perfect seed, treated 
 with slightly different chemicals and compounds, can be learned only 
 by repeated and varied experiment." 1 As will be seen from later 
 studies described in this paper, this cautionary remark has been jus- 
 tified by the fact that no equally favorable result has been obtained 
 since 1906. 
 
 LIST OF OPERATIONS HERE REPORTED 
 1907 
 
 1. Field experiments with repellents, near Leroy, McLean county, 
 in charge of E. O. G. Kelly and J. J. Davis. 
 
 2. Field experiments with repellents by the Bloomington Canning 
 Company, near Normal, McLean county, reported by J. A. West. 
 
 3. Laboratory experiments made by J. J. Davis with the effect 
 on seed-corn produced by ordinary lemon oil, by lemon oil from which 
 the terpenes had been extracted, and by the terpenes themselves. 
 
 1908 
 
 4. Field experiments near Galesburg, Knox county, supervised by 
 J. A. West, but in immediate charge of G. E. Sanders. In these ex- 
 periments various repellents were applied to the seed, and the soil was 
 variously prepared for planting by plowing to different depths, by 
 disking different numbers of times, and by plowing in fall and spring. 
 A comparison was also made of infestation and injuries by root-lice 
 to a plot of corn on old oats-ground and to corn on old corn-ground. 
 
 1909 
 
 5. Field experiments near Bloomington, McLean county, in joint 
 charge of G. E. Sanders and W. P. Flint. This was essentially an ex- 
 
 Rep. State Ent. 111., p. 22. 
 
CORN ROOT-APHIS AND CONTROL OF ITS INJURIES 
 
 419 
 
 The inference that terpeneless oil of lemon, produced by distilling 
 off the more volatile terpenes from the ordinary oil, is more likely to 
 be injurious to seed-corn than either the terpenes or the crude oil, is 
 confirmed in an interesting manner by the results of experiments de- 
 scribed by Dr. Whitten in the paper already referred to, in which he 
 says : "At the present the trend of evidence tends to show that the 
 [corn] grains bear immersion in the lighter oils without injury for 
 much longer periods than in the heavier oils, and that the injurious 
 after-effects of the latter are more pronounced than those of the 
 former." 1 
 
 As a general conclusion from this phase of my discussion, it may 
 be said that my supposition that injury to planted seed-corn near 
 Bloomington was owing to differences in the quality of the oils applied 
 to the seed, was unfounded; and the cause of the observed variation in 
 the effects of treatment must be sought elsewhere. 
 
 As a further test of this conclusion we may take two sets of plant- 
 ings, made at the insectary, in which the seed was treated with the 
 same lemon oils, in mixtures of the same strengths, as were used by 
 Mr. W. R. Scott, of Knoxville, and Mr. Frank Clark, of De Long, two 
 Knox county farmers who reported serious injury to their seed. Sam- 
 ples of the oils were obtained from these farmers with statements of 
 the strengths used by them. Both bought their lemon oil in Knox- 
 ville, but from different druggists. From the following table it will be 
 seen that the insectary plantings of seed treated with these oils yielded 
 results not materially different from those of the untreated check- 
 plantings made at the same time ; and the injury reported must hence 
 have been due to some local cause. 
 
 POT PLANTINGS TREATED WITH ORDINARY LEMON OIL AND ALCOHOL AS USED 
 BY W. R. SCOTT AND FRANK CLARK. EXPERIMENT OF SEPTEMBER 22, 1907 
 
 
 MH 0) 
 
 Per cent of plants up 
 
 t! 
 
 Insectary test 
 
 6 * 
 
 
 _b/.O 
 
 v tn 
 
 
 
 
 * 
 
 September 
 
 October 
 
 > V 
 
 
 
 29 
 
 30 
 
 3 
 
 7 
 
 <. 
 
 Scott's sample 
 
 200 
 
 3 
 
 49 
 
 79 
 
 81 
 
 6 2 
 
 Clark's sample 
 
 600 
 
 2 
 
 21 
 
 76 
 
 79 
 
 5 5 
 
 Checks 
 
 250 
 
 
 
 31 
 
 81 
 
 83 1 6.1 
 
 Bulletin, Illinois State Laboratory of Natural History, Vol. X, Art. V, 
 p. 269. 
 
420 BULLETIN No. 178 [January, 
 
 CONTRIBUTING CAUSE OF INJURY TO SEED-CORN BY REPELLENTS 
 
 That the cause was indeed local is indicated by the fact that in a 
 prolonged trip, through central Illinois, made during the summer of 
 1907, for an inquiry concerning the use of lemon oil and its results, 
 Mr. Davis found a general complaint of injury to the seed in the 
 vicinity of Galesburg, arid especially between Knoxville and De Long. 
 In all of the territory covered by his trip the lemon-oil treatment had 
 been more or less used in practically all localities except in Christian 
 county, and there was commonly no report of injury to the seed, the 
 main complaint of the farmers being the fact that they found no dif- 
 ference in respect to thrift and stand between treated and untreated 
 corn. 
 
 What the local cause of injury probably was in these various cases 
 is shown by the record of rainfall at Bloomington, given on a preced- 
 ing page, taken in connection with the proof contained in Dr. Whit- 
 ten's studies, already referred to, that kerosene and other volatile oils 
 are injurious to seed-corn in proportion to the amount of moisture in 
 the ground during the planting and germinating period. In discussing 
 his own experiments, Dr. Whitten says : 
 
 "When the amount of water in the soil was reduced from 30% 
 saturation to 25 % saturation, the per cent, of germination was increased 
 and the growth of the seedlings was more nearly normal ; but when the 
 water content of the soil was increased to 50 or 75% saturation, the 
 per cent, of germination was markedly decreased and the subsequent 
 growth of many of the seedlings abnormal." Again he says : "It is 
 evident that within certain limits the seedlings are not injured by the 
 oil present at the time of planting, provided growth is initiated in the 
 presence of a minimum amount of water. The small quantities of 
 kerosene are toxic in proportion to the increase of the moisture con- 
 tent of the soil. In the 50 and 75 % saturated soils the dormant period 
 of the grain is always less than 36 hours, while in the 25% saturation 
 the time is extended to approximately five days. This increase of time 
 affords the seedling an opportunity to dispose of the oils much more 
 slowly, and it does so without injurious effects." 1 
 
 The Bloomington rainfall of nearly two and three-quarters inches 
 distributed over seven days and including the planting period of the 
 Normal field, must have kept the ground unusually moist from the be- 
 ginning, and is a sufficient explanation of the injury to seed-corn in 
 that field. Unfortunately, I can obtain no weather record of a place 
 
 'Bull. 111. State Lab. Nat. Hist., Vol. X, Art. V, pp. 266-267, 268. 
 
/9/5l CORN ROOT-APHIS AND CONTROL OF ITS INJURIES 421 
 
 where no injury was done, for comparison with the Bloomington ob- 
 servations, and to that extent the proof must remain incomplete. 
 
 FIELD EXPERIMENTS WITH REPELLENTS, 1907 
 
 I have next to report the purely negative results of a series of 
 field experiments and observations begun in April, 1907, at Le Roy, 
 McLean county, by one of my field assistants, Mr. E. O. G. Kelly, and 
 continued by Mr. John J. Davis, to whom the problem was transferred 
 in the latter part of June. In these experiments, intended as a partial 
 repetition and verification of those made at Elliott, in Ford county, in 
 1906, 1 no injury was done to the seed by oil of lemon and alcohol, oil 
 of citronella and alcohol, carbolic acid, pure kerosene, or pure turpen- 
 tine, each applied in the proportions commonly used by us at this 
 time; nor was any difference discernible between experimental and 
 check plots in the degree of infestation by the ants or by the aphids. 
 Both the observers^ atttributed the results to heavy flooding rains 
 which fell at intervals during the whole planting-period, and which 
 washed away the fluid repellents so thoroly that the seed no longer 
 smelled of them. At the same time root-lice virtually disappeared 
 from fields which had been especially selected for experiment because 
 they were so heavily infested by ants before planting that it seemed 
 certain that the corn would be seriously injured by root-lice unless it 
 was artificially protected. Rains fell here, in^short, at a time and in an 
 amount both to drown out the root-lice and to wash away the re- 
 pellents before the seed could be injured. 
 
 The following is an outline of the more important of these ex- 
 periments. 
 
 Experiment 1. A field of thirty acres, on which corn was grown 
 in 1906, preceded by oats in 1905. The seed used in planting was 
 dealt with as follows : that for 16 rows, was treated with a fourth 
 of an ounce of kerosene to the gallon of seed ; for 24 rows, with a 
 half ounce of kerosene to the gallon; for 68 rows, untreated and re- 
 served as a check ; for 44 rows, treated with three-fourths of an ounce 
 of kerosene; for 62 rows, with three ounces per gallon of a mixture 
 of oil of lemon (10 per cent) and alcohol (90 per cent) ; and for 10 
 rows, untreated, as an additional check. 
 
 The field was planted on the llth of May, 1907, and on the 20th 
 of May no odor of kerosene or oil of lemon could be detected on the 
 treated seed. On the 28th of May, many hills were burrowed by ants, 
 but an examination of fifty such hills, dug up for the purpose, dis- 
 
 Rep. State Ent. 111., p. 14. 
 
422 
 
 BULLETIN No. 178 
 
 [January, 
 
 closed no root-lice. On the 31st of May a few root-lice were found. 
 On the 6th of June an examination of two hundred hills dug up gave 
 the following averages: 
 
 Check plots, 50 hills examined. Six hundred and thirty-eight 
 adult ants, no ant larvae, 7 root-lice. 
 
 Plot treated with half an ounce of kerosene to the gallon of seed, 
 50 hills examined. Two hundred and ninety-four adult ants, 400 
 larvae, no root-lice. 
 
 Plot treated with three-fourths of an ounce of kerosene to the 
 gallon of seed, 50 hills examined. Six hundred and forty-one adult 
 ants, 500 larvae, 14 root-lice. 
 
 Plot treated with a 10 per cent solution of oil of lemon at the rate 
 of three ounces per gallon of seed, 50 hills examined. Seven hundred 
 and thirty-two adult ants, 400 larvae, 26 root-lice. 
 
 Taking the four plots together, 2,305 adult ants and 1,300 ant 
 larvae were found in two hundred hills, but these were accompanied by 
 only 47 root-lice. The last of June a large number of hills were dug 
 up in this field, but no root-lice were found. No injury was done to 
 the seed, and a good crop of corn was produced. 
 
 LEROY EXPERIMENT, EXAMINATION OF JUNE 6, 1907 
 
 Quantities per gallon of corn 
 
 No. hills 
 examined 
 
 Adult 
 ants 
 
 Ant larvae 
 
 Root-lice 
 
 None (check) 
 
 50 
 
 638 
 
 
 
 7 
 
 l /2 oz. kerosene 
 
 SO 
 
 294 
 
 400 
 
 
 
 54 oz kerosene 
 
 SO 
 
 641 
 
 500 
 
 14 
 
 3 oz. 10% solution oil of lemon. 
 
 50 
 
 732 
 
 400 
 
 26 
 
 Experiment 2. A 40-acre field, in corn the preceding year, was 
 selected because of the abundance of ants' nests noticed in following 
 the plow, these averaging a hundred nests to the mile of furrow. As 
 the plow used turned a 14-inch furrow, the above number of nests per 
 mile was approximately equivalent to seven hundred per acre. The 
 field was planted May 9 and 10, 24 rows with seed treated with three- 
 fourths of an ounce of turpentine to a gallon of seed; 24 rows with 
 half an ounce of turpentine to the same ; 16 rows with two ounces of a 
 10 per cent alcoholic solution of oil of lemon to the gallon; 20 rows 
 with three ounces of the same to the gallon; and 32 rows with three 
 ounces of a 10 per cent solution of oil of citronella to the gallon. 
 
 The seed in this field had begun to grow on the 17th of May, and 
 ants were found at this time in the checks but not in the treated plots. 
 
CORN ROOT-APHIS AND CONTROL OF ITS INJURIES 
 
 423 
 
 On the 6th of June, on the other hand, ants were found in practically 
 every one of three hundred hills examined in the various experimental 
 plots, the numbers varying from 1,657 to 4,163 adults to each lot of 
 fifty hills, and the ant larvae from 850 to 2,500. Root-lice, on the 
 other hand, varied from 2 to 241 to each lot of fifty hills. The totals 
 of these insects for the three hundred hills are as follows : adult ants, 
 16,935; ant larvae, 10,200; root-lice, 776. 
 
 The following table summarizes Mr. Davis's observations on the 
 condition of the field September 17. 
 
 FINAL TABLE, EXPERIMENT No. 2 
 
 
 
 CO 
 
 CO 
 
 M 
 
 
 
 J^ J3 
 
 <n n^ 
 
 ~ J2 
 
 
 
 jg IS 
 
 !3g 
 
 rt ^j 
 
 Treatment 
 
 ** G 
 
 ig 
 
 ug 
 
 c o 
 
 
 S 
 rt 
 
 
 
 
 
 . 4-1 
 
 
 
 O ^ 
 
 *"" 
 
 
 
 nJ <- 
 
 
 fc v 
 
 * 
 
 
 
 
 None (check) 
 
 200 
 
 149 
 
 140 
 
 9 
 
 Lemon oil 
 
 100 
 
 130 
 
 131 
 
 2 
 
 Oil of citronella 
 
 50 
 
 150 
 
 152 
 
 1 
 
 Turoentine , 
 
 100 
 
 141 
 
 133 
 
 8 
 
 Experiment 3. A field of forty acres, the planting of which began 
 May 28, but was interrupted by rain, and recommenced May 30, but 
 again interrupted by rain. On the 6th of June, owing to the wetness 
 of the weather, fifteen acres of this field still remained to be planted; 
 and during the night between the 6th and 7th it rained again. This 
 remaining part of the field was presently planted with seed treated 
 with a 10 per cent alcoholic solution of oil of lemon, three ounces of 
 the mixture to the gallon of seed. 
 
 On the 26th of June ants were numerous in this field, but no root- 
 lice were found. On the 3d of July thirty hills contained 300 adult 
 ants, 175 larvae, and 125 root-lice. October observations showed no 
 difference between the treated and the untreated parts of the field, 
 either in condition or in yield. 
 
 Experiment 4. Field planted on the llth of May with seed 
 treated with carbolic acid at the rate of three ounces per gallon of a 
 solution in water, containing 2 l /2 to 3 per cent of the acid. 
 
 On the 15th of June a hundred hills infested with ants in this 
 field were dug up, and root-lice were found in only six of them. Later 
 counts of the stand showed no difference between the treated and the 
 untreated plots, and neither injury nor benefit had resulted from the 
 treatment. 
 
424 BULLETIN No. 178 [January, 
 
 Experiment 5. A farmer's experiment in which a field of sweet 
 corn was planted June 12 and 13 in alternating strips with untreated 
 and with treated seed, oil of lemon being used, a pint to a gallon of 
 wood alcohol, and about three ounces of the mixture to the gallon 
 of corn. 
 
 June 26 the corn was above the ground, and on the 5th of July 
 ' a hundred hills were dug up and examined, with the result that 2,205 
 adult ants, 2,070 larvae and pupae, and 763 root-lice were found in the 
 untreated part of the field, while in the treated part the adult ants 
 numbered 1,215, the larvae and pupae 11, and the root-lice 282. From 
 this it appears that there was some repellent effect in the seed-corn 
 treatment in this field; but the weights of corn from an equal num- 
 ber of hills from treated and untreated plots showed no tangible dif- 
 ference in the yield, the ears from four rows of each weighing 
 between 2,100 and 2,200 pounds. 
 
 The Spring Weather at Leroy. No precise data of rainfall at 
 Leroy were obtainable for May and June, 190?, but the notes of the 
 field assistants are plain upon this point, as shown by the following 
 extracts : 
 
 May 2 and 3, work in corn fields interrupted by rain. 
 
 May 14, rained hard, packing the ground. 
 
 May 17, heavy rain here at night. Hard rains have apparently 
 hejd the root-lice back. 
 
 May 22, ground packed by hard rains and subsequent baking. 
 
 May 28, rain stopped planting. "Big, heavy rains seem to have 
 killed the plant-lice. Have noticed reduction, in short, after each 
 heavy rain." 
 
 May 30, cold and rains have reduced numbers of root-lice. 
 
 May 31, rain preceding night interrupted corn planting. 
 
 June 5, rain interrupted corn planting. 
 
 June 6, recent rains have made fields too wet to plant. 
 
 June 7, rained last night. 
 
 June 9, wet weather doubtless the cause of poor condition of 
 corn. 
 
 June 10, big storm. 
 
 June 22, observations stopped by rain. 
 
 Tune 26, corn in low ground apparently killed by water. 
 
 June 27, field too wet to cultivate. 
 
 July 9, corn on untilled field very poor because of wet weather. 
 
 The fields under observation and experiment were planted May 
 9, 10, 11, 13, and 14; May 22, 23, 28, and 30; and June 11, 14, 18, 
 and 19. 
 
/9/5] CORN ROOT-APHIS AND CONTROL OF ITS INJURIES 425 
 
 Why heavy damage should have been done to seed-corn at Nor- 
 mal because of rains, while rainy weather did no such harm at Leroy 
 or Chenoa, it is impossible now to determine for the lack of more 
 specific information concerning the situation at those places. 
 
 LABORATORY EXPERIMENTS WITH THE EFFECTS OF REPELLENTS 
 
 ON ANTS 
 
 The substances used in 1907 and 1908 in field experiments against 
 the corn-field ant had proved unsatisfactory, partly by reason of the 
 uncertainty of their effect on the insects, but largely also because of 
 the injury to seed-corn in wet weather. In the case of the oil of 
 lemon an additional difficulty was an insufficient supply of the oil 
 and the consequent certainty that the price would be put up to a 
 prohibitive figure if there was anything like a general demand for it 
 at planting time. A considerable series of experiments on ants was 
 consequently undertaken in the beginning of 1909 with a large 
 variety of possibly available repellents, with a view to a selection of 
 those most efficient and most readily obtainable, for further use in 
 the field. As it was desirable that the repellent effect should be got 
 without the substance chosen actually touching the seed, the fluids, 
 were mixed with sand or other similar substance of a kind to be 
 applied in the field by means of a fertilizer-dropper attached to the 
 planter and dropping a powdered fertilizer beside or over the hill. 
 
 All the experiments reported in this section were made by Mr. 
 Maurice C. Tanquary, a temporary assistant of the office, also, at the 
 time, a graduate student in the University of Illinois. His work 
 began January 13, 1909, and was carried on at irregular intervals 
 until the 30th of the following June. In all of them, established 
 colonies of ants were used, each consisting of worker ants and larvae, 
 and sometimes containing also a queen. As many previous experi- 
 ments with the corn-field ant had shown that it has a strong prefer- 
 ence for orange light, in which, altho its movements can be plainly 
 seen by us, it seems to act as if it were itself in the dark, and as the 
 worker ants are extremely devoted to the care of the larvae of their 
 species, an apparatus was arranged which should take advantage of 
 these two facts to afford a place of comfortable and attractive resort 
 such that the repellent effect of the substances tested might be shown 
 by driving the ants from these comfortable quarters into others less 
 desirable. It was thought especially that, if they were forced to 
 desert their larvae, the distance to which they were driven by the 
 repellents and the length of time elapsing before they returned to the 
 
426 
 
 BULLETIN No. 178 
 
 [January, 
 
 care of their helpless charges, would enable us to compare the various 
 substances tested in respect to the intensity and persistence of their 
 repellent effects. 
 
 The apparatus used (which we may call the cage, Fig. 1) was 
 essentially a shallow, water-tight glass tray, or basin, made by build- 
 ing a wall half an inch high, with putty covered by strips of glass, 
 around the edge of a pane of glass 16 X 12 inches, inside which another 
 pane of glass, 8 X 12 inches, was supported at the corners by pieces 
 of glass stuck on with balsam. This latter plate we will call the base 
 of the nest (b). Its top was a trifle below the upper edge of the walls of 
 the tray, so that water poured into the latter until it reached the 
 under-surface of the plate would surround it as by a moat, which 
 prevented the escape of the ants placed upon it. Under the center of 
 
 FIG. 1 
 
 the transparent bottom of the cage was placed a sheet of plain white 
 paper with concentric circles drawn upon it, the smallest a quarter 
 of an inch in diameter, and the succeeding circles separated from 
 each other by an eighth of an inch. By the aid of these circles one 
 could tell at a glance the exact distance from the center to which any 
 ant had withdrawn. Upon the center of the base was placed the 
 repellent, and over this a piece of orange glass, or cover, supported 
 at its corners by bits of cork just thick enough to allow the ants to 
 pass under the cover conveniently. The space between the cover and 
 the base is the nest (c). The orange covers differed in size from 2 X 2^ 
 inches to 2 l /z X 3, the latter being the size used in the following experi- 
 ments unless other dimensions are given in the descriptions. In some 
 of the cages used a circle three inches in diameter was cut out of the 
 
t9i 5] 
 
 CORN ROOT-APHIS AND CONTROL OF ITS INJURIES 
 
 419 
 
 The inference that terpeneless oil of lemon, produced by distilling 
 off the more volatile terpenes from the ordinary oil, is more likely to 
 be injurious to seed-corn than either the terpenes or the crude oil, is 
 confirmed in an interesting manner by the results of experiments de- 
 scribed by Dr. Whitten in the paper already referred to, in which he 
 says: "At the present the trend of evidence tends to show that the 
 [corn] grains bear immersion in the lighter oils without injury for 
 much longer periods than in the heavier oils, and that the injurious 
 after-effects of the latter are more pronounced than those of the 
 former." 1 
 
 As a general conclusion from this phase of my discussion, it may 
 be said that my supposition that injury to planted seed-corn near 
 Bloomington was owing to differences in the quality of the oils applied 
 to the seed, was unfounded ; and the cause of the observed variation in 
 the effects of treatment must be sought elsewhere. 
 
 As a further test of this conclusion we may take two sets of plant- 
 ings, made at the insectary, in which the seed was treated with the 
 same lemon oils, in mixtures of the same strengths, as were used by 
 Mr. W. R. Scott, of Knoxville, and Mr. Frank Clark, of De Long, two 
 Knox county farmers who reported serious injury to their seed. Sam- 
 ples of the oils were obtained from these farmers with statements of 
 the strengths used by them. Both bought their lemon oil in Knox- 
 ville, but from different druggists. From the following table it will be 
 seen that the insectary plantings of seed treated with these oils yielded 
 results not materially different from those of the untreated check- 
 plantings made at the same time; and the injury reported must hence 
 have been due to some local cause. 
 
 POT PLANTINGS TREATED WITH ORDINARY LEMON OIL AND ALCOHOL AS USED 
 BY W. R. SCOTT AND FRANK CLARK. EXPERIMENT OF SEPTEMBER 22, 1907 
 
 
 *4H CO 
 
 Per cent of plants up 
 
 " o 
 
 Insectary test 
 
 . c 
 
 O i-* 
 
 'Z v 
 
 
 t? O 
 
 <U </) 
 
 
 
 
 * 
 
 September 
 
 October 
 
 r> V 
 
 
 1 29 
 
 30 
 
 3 
 
 7 
 
 <.s 
 
 Scott's sample 
 
 200 
 
 3 
 
 49 
 
 79 
 
 81 
 
 6.2 
 
 Clark's sample 
 
 600 
 
 2 
 
 21 
 
 76 
 
 79 
 
 5 5 
 
 Checks 
 
 250 
 
 
 
 31 
 
 81 
 
 83 
 
 6.1 
 
 'Bulletin, Illinois State Laboratory of Natural History, Vol. X, Art. V, 
 p. 269. 
 
420 BULLETIN No. 178 [January, 
 
 CONTRIBUTING CAUSE OF INJURY TO SEED-CORN BY REPELLENTS 
 
 That the cause was indeed local is indicated by the fact that in a 
 prolonged trip through central Illinois, made during the summer of 
 1907, for an inquiry concerning the use of lemon oil and its results, 
 Mr. Davis found a general complaint of injury to the seed in the 
 vicinity of Galesburg, and especially between Knoxville and De Long. 
 In all of the territory covered by his trip the lemon-oil treatment had 
 been more or less used in practically all localities except in Christian 
 county, and there was commonly no report of injury to the seed, the 
 main complaint of the farmers being the fact that they found no dif- 
 ference in respect to thrift and stand between treated and untreated 
 corn. 
 
 What the local cause of injury probably was in these various cases 
 is shown by the record of rainfall at Bloomington, given on a preced- 
 ing page, taken in connection with the proof contained in Dr. Whit- 
 ten's studies, already referred to, that kerosene and other volatile oils 
 are injurious to seed-corn in proportion to the amount of moisture in 
 the ground during the planting and germinating period. In discussing 
 his own experiments, Dr. Whitten says : 
 
 "When the amount of water in the soil was reduced from 30% 
 saturation to 25% saturation, the per cent, of germination was increased 
 and the growth of the seedlings was more nearly normal; but when the 
 water content of the soil was increased to 50 or 75% saturation, the 
 per cent, of germination was markedly decreased and the subsequent 
 growth of many of the seedlings abnormal." Again he says: "It is 
 evident that within certain limits the seedlings are not injured by the 
 oil present at the time of planting, provided growth is initiated in the 
 presence of a minimum amount of water. The small quantities of 
 kerosene are toxic in proportion to the increase of the moisture con- 
 tent of the soil. In the 50 and 75% saturated soils the dormant period 
 of the grain is always less than 36 hours, while in the 25% saturation 
 the time is extended to approximately five days. This increase of time 
 affords the seedling an opportunity to dispose of the oils much more 
 slowly, and it does so without injurious effects." 1 
 
 The Bloomington rainfall of nearly two and three-quarters inches 
 distributed over seven days and including the planting period of the 
 Normal field, must have kept the ground unusually moist from the be- 
 ginning, and is a sufficient explanation of the injury to seed-corn in 
 that field. Unfortunately, I can obtain no weather record of a place 
 
 'Bull. 111. State Lab. Nat. Hist., Vol. X, Art. V, pp. 266-267, 268. 
 
/p/5] CORN ROOT-APHIS AND CONTROL OF ITS INJURIES 421 
 
 where no injury was done, for comparison with the Bloomington ob- 
 servations, and to that extent the proof must remain incomplete. 
 
 FIELD EXPERIMENTS WITH REPELLENTS, 1907 
 
 I have next to report the purely negative results of a series of 
 field experiments and observations begun in April, 1907, at Le Roy, 
 McLean county, by one of my field assistants, Mr. E. O. G. Kelly, and 
 continued by Mr. John J. Davis, to whom the problem was transferred 
 in the latter part of June. In these experiments, intended as a partial 
 repetition and verification of those made at Elliott, in Ford county, in 
 1906, 1 no injury was done to the seed by oil of lemon and alcohol, oil 
 of citronella and alcohol, carbolic acid, pure kerosene, or pure turpen- 
 tine, each applied in the proportions commonly used by us at this 
 time; nor was any difference discernible between experimental and 
 check plots in the degree of infestation by the ants or by the aphids. 
 Both the observers attributed the results to heavy flooding rains 
 which fell at intervals during the whole planting-period, and which 
 washed away the fluid repellents so thoroly that the seed no longer 
 smelled of them. At the same time root-lice virtually disappeared 
 from fields which had been especially selected for experiment because 
 they were so heavily infested by ants before planting that it seemed 
 certain that the corn would be seriously injured by root-lice unless it 
 was artificially protected. Rains fell here, in short, at a time and in an 
 amount both to drown out the root-lice and to wash away the re- 
 pellents before the seed could be injured. 
 
 The following is an outline of the more important of these ex- 
 periments. 
 
 Experiment 1. A field of thirty acres, on which corn was grown 
 in 1906, preceded by oats in 1905. The seed used in planting was 
 dealt with as follows : that for 16 rows, was treated with a fourth 
 of an ounce of kerosene to the gallon of seed; for 24 rows, with a 
 half ounce of kerosene to the gallon; for 68 rows, untreated and re- 
 served as a check; for 44 rows, treated with three-fourths of an ounce 
 of kerosene ; for 62 rows, with three ounces per gallon of a mixture 
 of oil of lemon (10 per cent) and alcohol (90 per cent) ; and for 10 
 rows, untreated, as an additional check. 
 
 The field was planted on the llth of May, 1907, and on the 20th 
 of May no odor of kerosene or oil of lemon could be detected on the 
 treated seed. On the 28th of May, many hills were burrowed by ants, 
 but an examination of fifty such hills, dug up for the purpose, dis- 
 
 '25th Rep. State Ent. 111., p. 14. 
 
422 
 
 BULLETIN No. 178 
 
 [January, 
 
 closed no root-lice. On the 31st of May a few root-lice were found. 
 On the 6th of June an examination of two hundred hills dug up gave 
 the following averages: 
 
 Check plots, 50 hills examined. Six hundred and thirty-eight 
 adult ants, no ant larvae, 7 root-lice. 
 
 Plot treated with half an ounce of kerosene to the gallon of seed, 
 50 hills examined. Two hundred and ninety-four adult ants, 400 
 larvae, no root-lice. 
 
 Plot treated with three-fourths of an ounce of kerosene to the 
 gallon of seed, 50 hills examined. Six hundred and forty-one adult 
 ants, 500 larvae, 14 root-lice. 
 
 Plot treated with a 10 per cent solution of oil of lemon at the rate 
 of three ounces per gallon of seed, 50 hills examined. Seven hundred 
 and thirty-two adult ants, 400 larvae, 26 root-lice. 
 
 Taking the four plots together, 2,305 adult ants and 1,300 ant 
 larvae were found in two hundred hills, but these were accompanied by 
 only 47 root-lice. The last of June a large number of hills were dug 
 up in this field, but no root-lice were found. No injury was done to 
 the seed, and a good crop of corn was produced. 
 
 LEROY EXPERIMENT, EXAMINATION OF JUNE 6, 1907 
 
 Quantities per gallon of corn 
 
 No. hills 
 examined 
 
 Adult 
 ants 
 
 Ant larvae 
 
 Root-lice 
 
 None (check) 
 
 SO 
 
 638 
 
 o 
 
 7 
 
 l /2 oz. kerosene 
 
 50 
 
 294 
 
 400 
 
 
 
 54 oz. kerosene 
 
 SO 
 
 641 
 
 500 
 
 14 
 
 3 oz. 10% solution oil of lemon. 
 
 50 
 
 732 
 
 400 
 
 26 
 
 Experiment 2. A 40-acre field, in corn the preceding year, was 
 selected because of the abundance of ants' nests noticed in following 
 the plow, these averaging a hundred nests to the mile of furrow. As 
 the plow used turned a 14-inch furrow, the above number of nests per 
 mile was approximately equivalent to seven hundred per acre. The 
 field was planted May 9 and 10, 24 rows with seed treated with three- 
 fourths of an ounce of turpentine to a gallon of seed; 24 rows with 
 half an ounce of turpentine to the same; 16 rows with two ounces of a 
 10 per cent alcoholic solution of oil of lemon to the gallon; 20 rows 
 with three ounces of the same to the gallon; and 32 rows with three 
 ounces of a 10 per cent solution of oil of citronella to the gallon. 
 
 The seed in this field had begun to grow on the 17th of May, and 
 ants were found at this time in the checks but not in the treated plots. 
 
CORN ROOT-APHIS AND CONTROL OF ITS INJURIES 
 
 423 
 
 On the 6th of June, on the other hand, ants were found in practically 
 every one of three hundred hills examined in the various experimental 
 plots, the numbers varying from 1,657 to 4,163 adults to each lot of 
 fifty hills, and the ant larvae from 850 to 2,500. Root-lice, on the 
 other hand, varied from 2 to 241 to each lot of fifty hills. The totals 
 of these insects for the three hundred hills are as follows : adult ants, 
 16,935; ant larvae, 10,200; root-lice, 776. 
 
 The following table summarizes Mr. Davis's observations on the 
 condition of the field September 17. 
 
 FINAL TABLE, EXPERIMENT No. 2 
 
 
 
 J2 
 
 jn 
 
 (A 
 
 
 M 
 
 ^ rz3 
 
 C/3 -VH 
 
 * V 4 
 
 
 rs "^ 
 
 "rt-C 
 
 rt* 1 * 
 
 ^ rs 
 
 Treatment 
 
 45 n 
 
 8 
 
 *H 1 
 
 
 
 *o E 
 
 o 
 
 
 
 Jj.^s 
 
 
 o ^! 
 
 "^ 
 
 O 
 
 132 
 
 
 " 
 
 121 
 
 s 
 
 pg 
 
 None (check) 
 
 200 
 
 149 
 
 140 
 
 9 
 
 Lemon oil 
 
 100 
 
 130 
 
 131 
 
 2 
 
 Oil of citronella 
 
 50 
 
 150 
 
 152 
 
 1 
 
 Turpentine 
 
 100 
 
 141 
 
 133 
 
 8 
 
 Experiment 3. A field of forty acres, the planting of which began 
 May 28, but was interrupted by rain, and recommenced May 30, but 
 again interrupted by rain. On the 6th of June, owing to the wetness 
 of the weather, fifteen acres of this field still remained to be planted; 
 and during the night between the 6th and 7th it rained again. This 
 remaining part of the field was presently planted with seed treated 
 with a 10 per cent alcoholic solution of oil of lemon, three ounces of 
 the mixture to the gallon of seed. 
 
 On the 26th of June ants were numerous in this field, but no root- 
 lice were found. On the 3d of July thirty hills contained 300 adult 
 ants, 175 larvae, and 125 root-lice. October observations showed no 
 difference between the treated and the untreated parts of the field, 
 either in condition or in yield. 
 
 Experiment 4. Field planted on the llth of May with seed 
 treated with carbolic acid at the rate of three ounces per gallon of a 
 solution in water, containing 2 l /2 to 3 per cent of the acid. 
 
 On the 15th of June a hundred hills infested with ants in this 
 field were dug up, and root-lice were found in only six of them. Later 
 counts of the stand showed no difference between the treated and the 
 untreated plots, and neither injury nor benefit had resulted from the 
 treatment. 
 
424 BULLETIN No. 178 [January, 
 
 Experiment 5. A farmer's experiment in which a field of sweet 
 corn was planted June 12 and 13 in alternating strips with untreated 
 and with treated seed, oil of lemon being used, a pint to a gallon of 
 wood alcohol, and about three ounces of the mixture to the gallon 
 of corn. 
 
 June 26 the corn was above the ground, and on the 5th of July 
 a hundred hills were dug up and examined, with the result that 2,205 
 adult ants, 2,070 larvae and pupae, and 763 root-lice were found in the 
 untreated part of the field, while in the treated part the adult ants 
 numbered 1,215, the larvae and pupse 11, and the root-lice 282. From 
 this it appears that there was some repellent effect in the seed-corn 
 treatment in this field; but the weights of corn from an equal num- 
 ber of hills from treated and untreated plots showed no tangible dif- 
 ference in the yield, the ears from four rows of each weighing 
 between 2,100 and 2,200 pounds. 
 
 The Spring Weather at Leroy. No precise data of rainfall at 
 Leroy were obtainable for May and June, 1907, but the notes of the 
 field assistants are plain upon this point, as shown by the following 
 extracts : 
 
 May 2 and 3, work in corn fields interrupted by rain. 
 
 May 14, rained hard, packing the ground. 
 
 May 17, heavy rain here at night. Hard rains have apparently 
 held the root-lice back. 
 
 May 22, ground packed by hard rains and subsequent baking. 
 
 May 28, rain stopped planting. "Big, heavy rains seem to have 
 killed the plant-lice. Have noticed reduction, in short, after each 
 heavy rain/' 
 
 May 30, cold and rains have reduced numbers of root-lice. 
 
 May 31, rain preceding night interrupted corn planting. 
 
 June 5, rain interrupted corn planting. 
 
 June 6, recent rains have made fields too wet to plant. 
 
 June 7, rained last night. 
 
 June 9, wet weather doubtless the cause of poor condition of 
 corn. 
 
 June 10, big storm. 
 
 June 22, observations stopped by rain. 
 
 Tune 26, corn in low ground apparently killed by water. 
 
 June 27, field too wet to cultivate. 
 
 July 9, corn on untilled field very poor because of wet weather. 
 
 The fields under observation and experiment were planted May 
 9, 10, 11, 13, and 14; May 22, 23, 28, and 30; and June 11, 14, 18, 
 and 19. 
 
/p/5] CORN ROOT-APHIS AND CONTROL OF ITS INJURIES 425 
 
 Why heavy damage should have been done to seed-corn at Nor- 
 mal because of rains, while rainy weather did no such harm at Leroy 
 or Chenoa, it is impossible now to determine for the lack of more 
 specific information concerning the situation at those places. 
 
 LABORATORY EXPERIMENTS WITH THE EFFECTS OF REPELLENTS 
 
 ON ANTS 
 
 The substances used in 1907 and 1908 in field experiments against 
 the corn-field ant had proved unsatisfactory, partly by reason of the 
 uncertainty of their effect on the insects, but largely also because of 
 the injury to seed-corn in wet weather. In the case of the oil of 
 lemon an additional difficulty was an insufficient supply of the oil 
 and the consequent certainty that the price would be put up to a 
 prohibitive figure if there was anything like a general demand for it 
 at planting time. A considerable series of experiments on ants was 
 consequently undertaken in the beginning of 1909 with a large 
 variety of possibly available repellents, with a view to a selection of 
 those most efficient and most readily obtainable, for further use in 
 the field. As it was desirable that the repellent effect should be got 
 without the substance chosen actually touching the seed, the fluids 
 were mixed with sand or other similar substance of a kind to be 
 applied in the field by means of a fertilizer-dropper attached to the 
 planter and dropping a powdered fertilizer beside or over the hill. 
 
 All the experiments reported in this section were made by Mr. 
 Maurice C. Tanquary, a temporary assistant of the office, also, at the 
 time, a graduate student in the University of Illinois. His work 
 began January 13, 1909, and was carried on at irregular intervals 
 until the 30th of the following June. In all of them, established 
 colonies of ants were used, each consisting of worker ants and larvae, 
 and sometimes containing also a queen. As many previous experi- 
 ments with the corn-field ant had shown that it has a strong prefer- 
 ence for orange light, in which, altho its movements can be plainly 
 seen by us, it seems to act as if it were itself in the dark, and as the 
 worker ants are extremely devoted to the care of the larvae of their 
 species, an apparatus was arranged which should take advantage of 
 these two facts to afford a place of comfortable and attractive resort 
 such that the repellent effect of the substances tested might be shown 
 by driving the ants from these comfortable quarters into others less 
 desirable. It was thought especially that, if they were forced to 
 desert their larvae, the distance to which they were driven by the 
 repellents and the length of time elapsing before they returned to the 
 
426 
 
 BULLETIN No. 178 
 
 [January, 
 
 care of their helpless charges, would enable us to compare the various 
 substances tested in respect to the intensity and persistence of their 
 repellent effects. 
 
 The apparatus used (which we may call the cage, Fig. 1) was 
 essentially a shallow, water-tight glass tray, or basin, made by build- 
 ing a wall half an inch high, with putty covered by strips of glass, 
 around the edge of a pane of glass 16 X 12 inches, inside which another 
 pane of glass, 8 X 12 inches, was supported at the corners by pieces 
 of glass stuck on with balsam. This latter plate we will call the base 
 of the nest (b). Its top was a trifle below the upper edge of the walls of 
 the tray, so that water poured into the latter until it reached the 
 under-surface of the plate would surround it as by a moat, which 
 prevented the escape of the ants placed upon it. Under the center of 
 
 FIG. 1 
 
 the transparent bottom of the cage was placed a sheet of plain white 
 paper with concentric circles drawn upon it, the smallest a quarter 
 of an inch in diameter, and the succeeding circles separated from 
 each other by an eighth of an inch. By the aid of these circles one 
 could tell at a glance the exact distance from the center to which any 
 ant had withdrawn. Upon the center of the base was placed the 
 repellent, and over this a piece of orange glass, or cover, supported 
 at its corners by bits of cork just thick enough to allow the ants to 
 pass under the cover conveniently. The space between the cover and 
 the base is the nest (c}. The orange covers differed in size from 2 X 2^ 
 inches to 2^/2 X 3, the latter being the size used in the following experi- 
 ments unless other dimensions are given in the descriptions. In some 
 of the cages used a circle three inches in diameter was cut out of the 
 
/9/5] CORN ROOT-APHIS AND CONTROL OF ITS INJURIES 427 
 
 center of the base, and this was filled with cement in a way to make 
 a disk which, being in contact with the water beneath, was always 
 moist. In these cages the orange cover was a circle of glass Z l / 2 
 inches in diameter. 
 
 The fluid repellents were commonly applied by saturating fine 
 sand with them and depositing this in a small pile at the center of the 
 nest. This was always done after the ant colony with its larvae in 
 charge had established itself beneath the orange cover. 
 
 The object of these experiments being merely to test the sub- 
 stances in a comparative way, the conditions were in all cases made 
 as nearly identical as practicable, especially with respect to heat and 
 light. It is nevertheless evident that they are subject to the disadvan- 
 tage that colonies of ants of the same species are not necessarily equal 
 and similar in their reactions, and that the same colony may not al- 
 ways react in the same way to the same treatment. One of the most 
 interesting of Mr. Tanquary's observations shows that the aspect of 
 the reaction may be considerably changed by the exceptional sensibil- 
 ity or activity of only a very few of the individual ants of a family 
 group only three or four, perhaps, out of as many hundred rising to 
 the occasion and rescuing the young from dangerous or offensive situ- 
 ations. 
 
 I have found no way of tabulating or otherwise condensing the 
 descriptions of Mr. Tanquary's notes, and can only give the main re- 
 sults of the tests in very general terms, referring the reader for fur- 
 ther information to the details of the observations. Generally speak- 
 ing, then, it seems from these experiments that oil of tansy, oil of 
 lemon, anise oil, tincture of asafetida, apterite, and vermicide are very 
 strongly repellent to the corn-field ant; that kerosene, camphor, and 
 coal-tar are strong repellents, and that the other substances tested are, 
 if repellent at all, too slightly so, or for too short a time, to make them 
 promising materials for any practical use. 
 
 Experiment 5768^, Check. January 13, 1.0:25 a. m., as a check 
 upon the other experiments, a little sand moistened with water was put 
 under an orange cover which had been removed for this purpose to a 
 fresh part of the base at the close of an experiment with oil of lemon. 
 The ants immediately began to assemble under the cover, carrying 
 their larvae with them ; but twenty-seven of the latter were thrown by 
 their nurses into the water, probably because they still smelled of the 
 lemon oil. Other ants began at once to carry out the sand grains and 
 
 1 The numbers here used are those of the "experiment record" of the office, 
 a book in which all experiments are permanently recorded. 
 
428 
 
 BULLETIN No. 178 
 
 [January, 
 
 scatter them about outside the nest. The ants were not repelled by the 
 moist sand, but seemed to dislike its physical properties. By 11:30 
 almost every particle of the sand had been removed, and the ants had 
 placed a few larvae on the square of tin on which the sand rested. By 
 1 : 30 p. m., all the sand removed, some of it being carried out and 
 thrown into the water. One of the three bunches of larvae under the 
 orange cover was now on the tin. Time, 3 hours and 5 minutes. 
 
 Experiment 5762, Kerosene. January 13, 1 : 50 p. m. A small 
 amount of sand moistened with kerosene was placed under the center 
 
 FIG. 2 
 
 of the orange cover. The ants nearest at once faced towards it, waved 
 their antennae about, and then ran around in confusion. A very few of 
 the ants approached the sand, and even touched it, but quickly jerked 
 back, throwing their antennae about vigorously, seemingly in great dis- 
 tress. Others circled completely around the sand at a distance of 
 one or two inches. After 1.5 minutes a few of the ants with some of 
 their larvae were bunched under one corner of the orange cover. In 
 55 minutes, about a fourth of the ants were under the edge of the 
 cover, another fourth were an inch and a half outside the cover, with 
 the queen, while the other half were assembled at a remote corner of 
 the base, as shown in the accompanying sketch (Fig. 2). January 
 14, 9:45 a. m. (19 hours, 5 minutes), situation about as on the previous 
 day, except that approximately half the ants were under the cover, 
 none of them, however, nearer than five-eighths of an inch to the re- 
 pellent. Most of the ants under the cover were in the neighborhood 
 of the queen, who was just an inch from the edge of the sand. The 
 
CORN ROOT-APHIS AND CONTROL OF ITS INJURIES 
 
 429 
 
 average distance of the ants from the outside edge of the sand was 
 one and an eighth inches, but the nearest ants were in an approximate 
 circle around the sand at a distance of five-eighths of an inch. (Fig 3.) 
 
 JW< 
 
 FIG. 3 
 
 Experiment 5771, Oil of Lemon. January 12, 4: 15 p. m. A lit- 
 tle sand moistened with oil of lemon was placed on the base, and the 
 orange cover was moved to bring its center over the sand. Within 
 three minutes nearly all the ants were out from under the cover, leav- 
 ing nearly all their larvae behind. A few of the latter which were so 
 far from the sand that the ants could get at them, were brought to- 
 gether near the edge of the nest. Some of the ants attempted to re- 
 move the remaining larvae, but when they came within an inch and a 
 quarter to an inch and a half of the sand they stopped, sometimes 
 with spasmodic jerkings of their antennae, and then turned back. 
 
 A larger orange cover, 4X5 inches, was placed over the sand and 
 left over night. 7:10 a. m. (14 hours, 55 minutes), no ants under the 
 cover, all being gathered along the edge of the base. The larvae were 
 still scattered about in the nest. 8 a. m., orange cover replaced by an- 
 other, 5X6 inches. 9 a. m., the ants would not go under the cover 
 except that an occasional one ran in for a moment at the edge. A still 
 larger glass, 6X8 inches, substituted for the preceding. 11 : 30 a. m., 
 the ants were all under one end of the cover, as far away as possible 
 from the sand, but they had not gathered up their scattered larvae. 
 The position was as shown by the following sketch (Fig. 4). The 
 ants nearest the center of the nest were constantly moving about, as 
 if dissatisfied, those nearer the edge being quiet. The large cover was 
 
430 
 
 BULLETIN No. 178 
 
 [January, 
 
 now removed, together with the repellent, and an orange cover 2fy X 3 
 inches was put in its place. On the following day, January 13, the 
 ants were all assembled in the nest. 
 
 Queen' 
 
 s/ 6"X 8" 
 
 FIG. 4 
 
 Experiment 5773, Oil of Lemon. April 26, 1.1 : 12 a. m. A small 
 amount of sand moistened with oil of lemon placed under the cover, 
 within five-eighths of an inch of a pile of larvae. The ants immediately 
 began to crowd away, about a sixth of the colony remaining under the 
 edge of the cover an inch from the sand, and the larvae being de- 
 serted for the time being. Four of the workers soon began to move 
 the larvae to the edge of the nest. During 32 minutes but four different 
 ants were seen carrying larvae. After 4 hours no ants remained under 
 the cover. They had removed most of the larvae to the edge of the 
 base, and three of the workers were engaged in carrying off the re- 
 mainder. Mr. Tanquary remarks that very often only a very small 
 number of the workers half a dozen or so were active in removing 
 the larvae from the neighborhood of the repellent. In 5 hours and 18 
 minutes all the larvae had been removed. In 15 minutes more some 
 ants were resting under the corner of the cover. April 27, 8 : 30 a. m., 
 no ants were under the cover. 9:15 (22 hours), about twenty ants 
 under one corner of the cover. An hour and 5 minutes later, about 
 two dozen ants were under the cover, one and an eighth inches from 
 the sand. 10 : 25, the orange cover replaced with a larger one, 5X6 
 inches, and food exposed at various points under it for the ants. 11 : 25, 
 not more than half the ants are yet under the cover. 11 : 50, most of 
 the ants are now in the nest. 3 : 30 p. m., the large glass replaced by 
 one 2 l /2 X 3 inches. 4 : 45, about half the ants are under the glass. 
 April 27, 9: 50 a. m., about two-thirds are under the cover with the 
 larvae, but the others are out on the edge of the base. 11:05, same 
 
CORN ROOT-APHIS AND CONTROL OF ITS INJURIES 
 
 431 
 
 situation as above. 11:24, about three-fourths of the ants are under 
 the cover. Repellent is removed and experiment closed. 
 
 Experiment 5776, Oil of Lemon. May 1, 11: 50 a. m., sand mois- 
 tened with oil of lemon placed under the orange cover half an inch 
 from the larvae. The ants scattered immediately, most of them leav- 
 ing the nest entirely, but a few remained at its corners. The larvae 
 were completely deserted. Five minutes later a few ants were under 
 each of three corners, and three or four were beginning to move the 
 larvae to the corner of the nest. Most of the ants were out on the 
 corners of the base, as shown in Figure 5. r 1 hour and 20 minutes, 
 
 FIG. 5 
 
 fewer ants under the cover, most of the larvae remaining in their origi- 
 nal position. 2 hours and 35 minutes, situation unchanged. In 3 hours 
 and 40 minutes about a fourth of the ants were under the cover, but 
 the larvae were not yet gathered up (Fig. 6). Four hours and 45 
 minutes, situation unchanged. May 3, 9 : 30, no ants under the cover, 
 but all clustered along the edges. 11 : 30 (23 hours and 40 minutes), 
 same situation. 3:05 p. m. (27 hours and 15 minutes),) about two 
 dozen ants under one corner of the cover. 5 p. m., no ants under the 
 cover. May 4, 9 a. m., 11 : 55 a. m., 3 p. m., and 5 : 15 p. m., situation 
 unchanged. The ants have not gathered up the larvae which they de- 
 serted in the beginning. May 5, 7 : 45, all the ants gathered around the 
 edge of the base. 8 : 10, about a dozen ants are under a corner of the 
 cover nearest the larvae. 1 1, : 30, a few of the larvae have been; gath- 
 ered up and transferred to a corner of the nest. 4: 40 p. m., about two 
 dozen of the ants under a corner of the orange cover with about a 
 
432 
 
 BULLETIN No. 178 
 
 [January, 
 
 fourth of the larvae, which they have gathered up. These larvae are an 
 inch and an eighth from the sand. May 6, 9 a. m., nearly all of the 
 ants are out on the edge of the base. About two-thirds of the larvae 
 have been brought together at a corner of the nest, and about a dozen 
 ants are with them. Occasionally another larva is brought over to the 
 corner. 1 1 : 30, situation unchanged. 2 p. m., a few more larvae have 
 been recovered. 5 : 30, about a dozen ants in the nest with larvae, not 
 all of which have yet been recovered. May 7, 8 : 20 a. m., most of the 
 larvae that had been moved to the corner of the nest are now out on 
 
 Ants arid Larvae 
 
 Ants 
 
 FIG. 6 
 
 the edge of the base, and there are no ants under the cover. 1 1 : 30 
 a. m., and 5 p. m., situation unchanged. May 8, 9 a. m., no ants under 
 the cover. Experiment closed. Total time nearly 7 days. [Mr. Tan- 
 quary's notes do not show that the ants were fed during this experi- 
 ment.] 
 
 Experiment 5772, Emulsion of Oil of Lemon. April 25, 3 : 50 
 p. m., small amount of sand moistened with a 5 per cent emulsion of 
 oil of lemon was placed under the cover. The ants gradually crowded 
 away from the sand. 4 p. m., the ants were three-eighths of an inch 
 from the sand, and were taking their larvae with them. 4:10, the ants 
 were half an inch from the sand. 4: 45, the ants were withdrawn an- 
 other eighth of an inch. 5 : 45, same distance from the sand, but not 
 so many under the cover. April 26, 9:30 a. m. (17 hours and 40 
 minutes), about half the ants were under the cover, half an inch from 
 the repellent. Larvae three-fourths of an inch distant. 10:45* a. m., 
 about two-thirds of the ants were under the cover, the nearest a fourth 
 
i9i 5\ 
 
 CORN ROOT-APHIS AND CONTROL OF ITS INJURIES 
 
 433 
 
 of an inch from the repellent. The experiment was closed by the re- 
 moval of the sand, the odor of which was scarcely distinguishable. 
 
 Experiment 5777 , Oil of Lemon. May 27, 2 : 37 p. m. This ex- 
 periment was made in a cage with a 3-inch cement disk at the center of 
 the base, and a circular orange cover 3^4 inches across. Sand mois- 
 tened with oil of lemon was placed beneath the center of the cover. 
 The ants were thrown immediately into great confusion, and about half 
 of them at first ran from under the cover, deserting for a time the 
 larvae nearest the sand. These were about one and a fourth inches from 
 the repellent. In 5 minutes the ants on the base were beginning to re- 
 turn beneath the orange cover, some moving the larvae farther from 
 the sand and recovering those at first deserted. After 10 minutes the 
 distance from the sand to the nearest larva was five-eighths of an inch. 
 They were still moving their larvae back. 3 : 08, nearest larva now 
 six-eighths of an inch. 3 : 40 (63 minutes), nearest larva seven-eighths 
 of an inch. Most of the ants are out on the base (Fig. 7, A). 5 and 
 
 V.i'.Ov Larvae 
 
 FIG. 7 
 
 5:30, situation unchanged. May 28, 8 a. m. (17 hours, 23 minutes), 
 larvae are more scattered, and the inner edge of the pile is about five- 
 eighths of an inch from the sand. About three- fourths of the ants 
 are under the cover with them. 2 and 5 : 30 p. m., nearest larvae six- 
 eighths of an inch from the repellent. May 29, 8 a. m. (41 hours, 23 
 minutes), nearly all the ants are under the cover. The nearest are 
 three-eighths of an inch from the repellent, as shown by Figure 7, B. 
 1.1 : 50 a. m. arid 1 : 30 p. m., situation unchanged. 5 : 45, ants now all 
 
434 
 
 BULLETIN No. 178 
 
 [January, 
 
 under the cover, but at the same distance from the repellent as before. 
 May 31, 8 a. m., and 3 : 30 p. m., situation unchanged. 6 p. m. (4 days 
 and 3*^5 hours), ants same distance from sand, but more dispersed 
 (Fig. 7, C). June 1, the ants move about somewhat but maintain their 
 distance from the repellent all day long. The same record was made 
 for June 2, at 8 a. m. and 3 p. m. (6 days), when the experiment was 
 closed. 
 
 Experiment 5774, Oil of Lemon and Bone Meal. February 24, 
 9:10 a. m., some bone meal soaked with oil of lemon was allowed to 
 dry, then moistened with water, and placed at the center of the nest. 
 Most of the ants escaped from under the cover, but a third of them re- 
 mained under one corner with the larvae, which were seven-eighths of 
 an inch from the bone meal (Fig. 8). In an hour and fifty minutes 
 
 FIG. 8 
 
 the ants were about five-eighths of an inch from the meal, and nearly 
 half of them were under the cover. 3 : 50 p. m., about half the ants are 
 under the cover, the nearest half an inch from the fertilizer. 4: 50 (? 
 hours, 40 minutes), situation unchanged. February 25, 8 a. m., most 
 of the ants are under the cover, the nearest about half an inch from the 
 fertilizer. 9:30 (24 hours, 10 minutes), ants withdrawn to about 
 three-fourths of an inch. 11 a. m., situation unchanged except that 
 fewer of the ants are outside on the base. 3:15 and 5 p. m., same ap- 
 pearance. 7:15, ants were about seven-eighths of an inch from the re- 
 pellent, and about half were now outside the nest. February 26, 8 
 a. m., ants from half an inch to five-eighths of an inch distant from the 
 repellent this morning. 3 : 30 and 4 : 50 p. m. (2 days, 7 hours, 40 
 
'9/5J 
 
 CORN ROOT-APHIS AND CONTROL OF ITS INJURIES 
 
 435 
 
 minutes), ants six-eighths to seven-eighths of an inch distant, about a 
 third of them outside. February 27, 8 a. m., about four-fifths of the 
 ants are under the cover at a distance from the repellent of three- 
 eighths to four-eighths of an inch. 4: 50 p. m. (3 days and nearly 8 
 hours), five-sixths of the ants now under the cover, the nearest three- 
 eighths to four-eighths of an inch from the repellent. Experiment 
 closed. 
 
 Experiment 5775, Oil of Lemon with Wood Ashes. February 24, 
 11:10 a. m., wood ashes soaked in oil of lemon, allowed to dry, and 
 moistened with water, placed at center of nest. Collection of larvae a 
 fourth of an inch from the repellent. Ants soon leave the immediate 
 vicinity, deserting the larvae. 11 : 30 (20 minutes), the nearest ants are 
 five-eighths to six-eighths of an inch from the ashes. They have not 
 gathered up the deserted larvae. About two-thirds of them are under 
 the cover distributed as shown in the accompanying sketch (Fig. 9). 
 
 Deserted La 
 
 FIG. 9 
 
 4: 50 p. m. (5 hours, 40 minutes), ants are now about seven-eighths of 
 an inch from the ashes, but the deserted larvae have not been recovered 
 (Fig. 10). February 25, 8 a. m. (20 hours, 50 minutes), the ants are 
 about three-eighths of an inch from the repellent, deserted larvae not 
 recovered. At 9 : 30 the ants are withdrawn to about three-fourths of 
 an inch. At 11 a. m., 3:15, and 5 p. m. (29 hours, 50 minutes), 
 same appearance. 7:15 p. m. (31 hours 5 minutes), ants about seven- 
 eighths of an inch from the repellent, and a larger number than before 
 are outside the nest. February 26, 8 a. m., ants five-eighths to six- 
 eighths of an inch distant from the repellent. 3 : 30 p. m., ants with- 
 
436 
 
 BULLETIN No. 178 
 
 [January, 
 
 drawn an inch and an eighth from the repellent, more than half of 
 them outside the nest. 4: 50 p. m., nearest ants an inch and an eighth 
 from the repellent, two-thirds of them outside the nest. February 27, 
 
 Deserted Larvae 
 
 FIG. 10 
 
 8 a. m. (2 days, 20 hours, 50 minutes), most of the ants are under the 
 orange cover, the nearest being four-eighths to five-eighths of an inch 
 from the repellent. 11 : 50 (3 days, 40 minutes), ants distant from the 
 repellent three-eighths to four-eighths of an inch. 4: 50 p. m. (3 days, 
 3 hours, 40 minutes), ants distant from four- to five-eighths of an inch. 
 Experiment closed. 
 
 Experiment 5778, Oil of Tansy. April 17, 8 : 30 a. m., sand 
 moistened with oil of tansy was placed at the center of a nest under 
 the orange cover with a fresh colony of ants. Within four minutes all 
 
 FIG. 11 
 
 the ants had left the nest, deserting a large pile of larvae except for a 
 few carried away as they escaped. 8 : 45, a number of the ants go into 
 the nest and walk about for awhile, but presently leave it, removing 
 none of the larvae. The position of the larvae in the nest is shown by 
 
/p/5] CORN ROOT-APHIS AND CONTROL OF ITS INJURIES 437 
 
 the preceding sketch (Fig. 11, A). 9:15, a few ants resting under 
 one corner of the cover with a small number of the larvae in charge 
 (Fig. 11, B). 10: 30 (2 hours), all the ants but two have left the nest, 
 deserting the larvae. 1.1 : 50, same situation. 4 p. m. (7 hours, 30 
 minutes), no ants under the cover. About one-third of their larvae 
 have been carried out to a corner of the base, but the others remain in 
 the nest. April 22, 2: 45 p. m. (5 days, 6 hours, 15 minutes), the ants 
 have remained during all this interval on the corner of the base with a 
 small part of their larvae, and have not gone near the nest. A few of 
 them were apparently killed by the tansy oil. Repellent removed, the 
 sand still smelling very strongly of the oil. 
 
 Experiment 5779, Oil of Tansy. April 22, 2 : 28 p. m., sand satu- 
 rated with oil of tansy placed at the center of a nest. The ants scattered 
 precipitately, deserting the larvae and many of them falling into the 
 water around the base. Seventeen of the ants, some of which in the 
 confusion rushed against the sand were killed by the oil of tansy. The 
 others scattered over the base. 3:10 p. m. (42 minutes), seven ants 
 under one corner of the cover. 3 : 45, 4 : 35, and 5 : 10, no ants under the 
 cover. April 23, 9 a. m. (18 hours, 32 minutes), no ants under the 
 cover. 11:30 a. m. (21 hours, 2 minutes), three or four ants went 
 now and then for a little time into one corner of the nest. 3 : 05 p. m., 
 about two dozen of the ants had gathered up most of the larvae under 
 one corner of the cover an inch and an eighth from the repellent. All 
 the other ants were out on the base. April 24, 8 and 11, a. m. (2 days, 
 8 hours, 32 minutes), no ants were in the nest. The larvae in the cor- 
 ner of the nest yesterday were piled on a corner of the base. The 
 repellent was removed, the odor still quite strong. The small cover 
 was replaced by an orange glass 4X5 inches, and food was placed at 
 the center of the nest. 2: 30 p. m., nearly all the ants had gathered in 
 the nest with their larvae. 
 
 Experiment 5789, Tansy Tea. May 24, tansy tea was prepared 
 by boiling an ounce of dry tansy leaves for fifteen minutes in a quart 
 of water. The ants paid almost no attention to sand moistened with 
 this infusion, but gathered around it as if it were not in the least ob- 
 jectionable. May 25, 10: 30 a. m., same situation, all the ants being in 
 the nest. Experiment closed. 
 
 Experiment 5741, Tincture of Asafetida.Mzy 4, 1909, 9:25 
 a. m., sand moistened with asafetida was placed at the center of a nest. 
 The ants within began immediately to scatter, most of them going out 
 on the base, but some of them rushing back and forth under the orange 
 cover. At 9:45 (20 minutes), a few were still running about in the 
 
438 BULLETIN No. 178 [January, 
 
 nest, but eight were lying on their backs near the repellent, apparently 
 overcome by the odor. At 10: 05 (40 minutes), practically all the ants 
 were out on the base, some of those that were overcome struggling 
 about, unable to escape. 11 a. m., eleven ants were apparently dead 
 in the nest. At 11: 55, fourteen dead ants were seen under the cover. 
 By 3:1.5 several of those overcome had either recovered or had been 
 carried out. At 5:15 (7 hours, 50 minutes), no ants were in the nest. 
 The same entry was made at intervals from May 5 at 9 a. m. to May 8, 
 no ants having entered the nest at any time during this interval of 
 four days from the beginning of the experiment. 
 
 Experiment 5744, Anise Oil. June 30, 1909, 10 : 50 a. m. In this 
 experiment a large nest with a cement bottom was used with a cover 
 3^4 inches across. Sand moistened with anise oil was placed at the 
 center of the nest. The ants scattered immediately, deserting their 
 larvae, which were in two piles two-eighths and six-eighths of an inch, 
 respectively, from the repellent. At 11 o'clock five ants were under 
 the glass about the pile of larvae which was farthest from the sand, 
 and others were occasionally running about under the cover. At 1 1 : 30 
 the larvae most distant from the sand had been moved out on the base, 
 and no ants were now under the cover. At 5 p. m. (6 hours, 10 
 minutes), all the larvae had been removed from the nest and no ants 
 were under the cover. July 7(1 week) ; up to this time no ants had 
 returned to the nest. This was a weak colony, however, and the test 
 with anise oil should have been made again with a larger number of 
 ants. 
 
 Experiment 5748, Gum Camphor. January 29, 11 a. m., gum 
 camphor, cut up into fine particles and moistened with water, was 
 placed at the center of a nest. The ants scattered immediately, many 
 of them running about over the base but most of them hovering over 
 the larvae about three- fourths of an inch within the nest. At 11 :15 a 
 few ants were under the corners of the cover nearest the larvae. At 
 11: 50 most of the ants had gone outside the nest, clustering around 
 the larvae, but a few were under one corner of the cover, and two 
 small companies were farther out on the base. At 1 : 50 p. m. (2 hours, 
 50 minutes), about one-fourth to one-fifth of the ants were under the 
 cover, the nearest seven-eighths of an inch from the repellent. The 
 ants were in two companies, one near the nest and the other at a cor- 
 ner of the base (Fig. 12, A) ; and at 5:30 (6 hours, 30 minutes) the 
 situation was unchanged. On the following day, January 30, at 10 : 45 
 a. m. (23 hours, 45 minutes), about half the ants were gathered along 
 
CORN ROOT-APHIS AND CONTROL OF ITS INJURIES 
 
 439 
 
 one edge of the cover (Fig. 12, B) and the others were in two com- 
 panies on the base. 
 
 FIG. 12 
 
 Experiment 5753, Gum Camphor in Solution. April 20, at 10 : 35, 
 sand soaked with a saturated watery solution of gum camphor was 
 
 Deserted Larvae 
 
 Ante and Ltrrac 
 
 FIG. 13 
 
 placed at the center of a nest. The ants immediately left the vicinity, 
 some remaining under the edge of the cover and the remainder escap- 
 
440 BULLETIN No. 178 [January, 
 
 ing from the nest. The larvae, which were four-eighths of an inch 
 from the sand, were deserted (Fig. 13, A). At 11. o'clock about 
 one-third of the ants were in the nest, as shown in the figure, the near- 
 est of them five-eighths of an inch from the repellent. At 11 : 15 a. m., 
 1 : 30 and 2 : 25 p. m. 3 hours, 50 minutes the nest presented practi- 
 cally the same appearance. At 3 : 45 (5 hours, 10 minutes), nearly all 
 of the ants had left the nest and a few of the larvae had been carried 
 to its outer edge (Fig. 13, B). At 4: 45 and at 5: 50 7 hours, 15 min- 
 utes about a dozen ants were still in the nest. April 21, at 9:30 
 a. m., no ants were in the nest, the larvae having all been carried out- 
 side. At 11 : 30 (24 hours, 55 minutes), several ants had moved under 
 the cover as shown in the sketch. At 3 : 30 and 5 p. m. the situation 
 was unchanged. By 8: 20 a. m. April 22 (45 hours, 45 minutes), about 
 three-fourths of the ants were in the nest, filling it half way; at 1.1 
 a. m. (48 hours, 25 minutes) the situation was unchanged, and the 
 experiment was closed. 
 
 Experiment 5758, Formic Acid. January 14, at 10 : 30, a small lot 
 of sand mixed with formic acid was placed on the base, and the orange 
 cover was moved over it to form a nest with the repellent at its center. 
 The ants presently began to move into the nest, but were immediately 
 affected by the odor of the acid. Only two approached the sand near 
 enough to touch it, and these jerked quickly back, vigorously rubbing 
 their antennae, which had been brought in contact with the acid. At 
 10:45 the queen of the colony entered the nest and the workers were 
 moving their larvae, all keeping as close to the borders of the nest as 
 practicable, the innermost of the assembly being always restless and 
 active. At 1.1:30 and at 11: 55 (1 hour, 25 minutes), the ants were 
 clustered at each of the four corners of the cover. At 3:10 p. m. (4 
 hours, 40 minutes), nearly all the ants were in the nest, a few nearer 
 the sand than before, the nearest within two-eighths to three-eighths 
 of an inch. Some occasionally crossed the clear space within the cir- 
 cle, and occasionally one even crawled over the sand, seemingly un- 
 affected by its odor. By 8:10 the next morning the ants were paying 
 no attention whatever to the sand, which was removed. It had not 
 the slightest perceptible odor, formic acid being highly volatile. 
 
 The experiment was repeated at 8 : 20 a. m. of this day, January 
 15, the ants immediately scattering, about one-third of them retreat- 
 ing to a corner of the base. At 8 : 35 the ants were collected in two of 
 the corners of the nest, the queen among them, and under the edge of 
 the cover farthest from the repellent, the nearest an inch and an 
 
CORN ROOT-APHIS AND CONTROL OF ITS INJURIES 
 
 441 
 
 eighth distant. The general appearance is illustrated by the follow- 
 ing sketch (Fig. 14). At 9: 10 and 10:25 fewer ants were under the 
 
 'Larvae 
 
 Queen 
 
 FIG. 14 
 
 cover, and the circle formed by them was somewhat larger. At 1 : 30 
 the distance between the sand and the nearest ants was six-eighths of 
 an inch, and a few more had entered the nest. At 3 p. m. (6 hours, 40 
 minutes), about half the ants were under the cover, the nearest to the 
 
 FIG. 15 
 
 repellent being three-eighths to four-eighths of an inch away (Fig. 
 15). Two ants were seen to touch the sand with no ill effects. Ex- 
 periment closed. 
 
442 
 
 BULLETIN No. 178 
 
 [January, 
 
 Experiment 5750, Coal-tar. March 15, at '3:50 p m., a small 
 amount of coal-tar was placed at the center of a nest under the orange 
 cover. The ants began to leave the nest at once, but only gradually. 
 In an hour and forty minutes all were out of the nest except about a 
 dozen which remained with the larvae, seven-eighths of an inch from 
 the tar. Half an hour later the ants were carrying these larvae outside. 
 By the following morning at 8: 30 (16 hours, 40 minutes), about fifty 
 ants were in one corner of the nest, distant five-eighths of an inch 
 from the repellent, and this condition remained unchanged thru this 
 day. Twenty-four hours later about a fourth of the ants were in the 
 nest, but during this day they began to withdraw again, and by 8 a. m. 
 of March 18 all were out of the nest but two, which with a few of 
 the larvae were one and a fourth inches from the tar, the other larvae 
 being outside on the base. By 1 : 30 of this day these larvae had all 
 been removed, and there was no further change until 8 : 30 of the 19th 
 (3 days, 16 hours), when the ants began to return, about half of them 
 being in the nest a fourth of an inch or more from the tar by 11.: 50 of 
 that day. Two days later, six days from the beginning of the experi- 
 ment, about half the ants were under the cover, together with the 
 larvae. 
 
 Experiment 5743, Apterite. March 5, at 11:35 a. m., apterite 
 moistened with water was placed at the center of a nest. The ants 
 were at first not very strongly repelled, but soon began to carry their 
 
 FIG. 16 
 
 larvae towards the edge of the nest. By 3 :15 all the workers were out- 
 side the nest except four, which were at one corner. Half of the 
 
/p/5] CORN ROOT-APHIS AND CONTROL OF ITS INJURIES 443 
 
 others were just outside on the edge of the nest, and the remainder on 
 one corner of the base. Most of the larvae had been carried out, al- 
 tho a number between an eighth and a fourth of an inch from the 
 tar had been left. (Fig. 16.) There was no return of the ants to this 
 nest up to March 11, 6 days after the experiment was started. During 
 all this period the colony stayed together on a distant corner of the 
 base, so closely packed that a number were crowded off into the sur- 
 rounding water every day and drowned. When the experiment closed, 
 March 11, only about sixty ants were alive. 
 
 Experiment 5790, Vaporite. March 5, at 11:30, a bit of moist 
 vaporite at the center of a nest disturbed the ants but did not repel 
 them violently. They were mostly outside the nest together with their 
 larvse when this was established, and by 3:15 only half a dozen ants 
 had gone under the cover. The rest remained outside until 10 : 45 the 
 following day, when about twenty were seen at one corner of the nest 
 two and a quarter inches from the repellent. By 4:15 of that after- 
 noon (28 hours, 45 minutes), there were about fifty ants in the nest, 
 the nearest one and a half inches from the vaporite, but all the larvae 
 were still outside on the base. The ants now gradually returned, bring- 
 ing their larvae with them, until at 9 a. m. of March 7 they were all 
 in the nest. The repellent was not removed until 8 : 45, March 11, nearly 
 six days after the experiment was begun. At this time the ants nearest 
 the vaporite were three-eighths of an inch away. 
 
 Experiment 5791, Vermicide. April 14, at 8:15 a. m., sand 
 soaked with vermicide and tested on a fresh colony, which had been in 
 the cage for five days only from the field, drove them out in less than 
 a minute, many of their larvae being left behind together with five of 
 the workers which had touched the vermicide and had then died. In 
 fifteen minutes the ants were beginning to carry their larvae out from 
 under the cover, and piling them along the border of the nest, as 
 shown in the following sketch (Fig. 17). By 3 p. m. there was 
 nothing in the nest except some deserted larvae (Fig. 18), and these 
 conditions remained unchanged until two days had elapsed, when at 
 8 : 50 a. m. April 16, a 4 X 4 cover was substituted for the smaller one. 
 The ants paid no attention to this change, and the next day at 8 : 20 
 a. m. a still larger orange cover 5X6 inches was put in place. This 
 brought certain of the ants under its protection at one corner, and 
 others moved under slowly until at 9 : 30 about one-third of the colony 
 were in the nest, the nearest two and a fourth inches from the repel- 
 lent. This condition remained practically unchanged until 1 1 : 25 April 
 19 (5 days, 3 hours), when the small orange cover with which the ex- 
 
444 
 
 BULLETIN No. 178 
 
 [January, 
 
 periment began was replaced. The sand seemed to have about as 
 much odor as at first. The ants, however, began to move under slowly, 
 
 *^^&^}S 
 
 $$&#" 
 
 ' & Deserted LA rvae 
 
 f 
 
 FIG. 17 
 
 and at 10 : 30 April 20, some three-fourths of them were in the nest. 
 Experiment closed. 
 
 '?*, 
 
 m 
 
 -- '>' 
 
 Deserted Larvae 
 
 FIG. 18 
 
 Experiment 5752, Carbon Bisulfid. March 26, this material, ap- 
 plied as usual, drove the ants immediately out of the nest, but owing to 
 its volatility it soon lost its effect, and two hours and twenty minutes 
 later they were practically all back, continuing, however, to avoid the 
 immediate vicinity of the sand for several days. 
 
79/5] CORN ROOT-APHIS AND CONTROL OF ITS INJURIES 445 
 
 Experiments were made with a considerable number of additional 
 repellents, to which the ants reacted so feebly or for so short a time 
 that a detail of their behavior is unnecessary. Among these were 
 pyrethrum powder, calcium carbide, capsicum, iron sulfate, chlorid of 
 lime, and tobacco, the last applied in the form of a small piece of to- 
 bacco plug which had been soaked in water. In the same class of sub- 
 stances which were more or less disagreeable to the ants, but never- 
 theless ineffective as repellents, were the following fertilizers: ground 
 limestone, rock phosphate, acid phosphate, ground sheep-manure, 
 kainit, ammonium sulfate, dried blood, bone meal, potassium sulfate, 
 sodium nitrate, and tankage the last, a vile-smelling material from 
 the slaughter-house, so little offensive to the ants that many f them ap- 
 proached and crawled over it freely, and even placed their larvae in 
 contact with it. Later, they dealt with this material as they did in an- 
 other case with sand that is, they carried it out of the nest and de 
 posited it on the glass outside or threw it into the water around their 
 cage. By 1:15 p. m. the nest had been cleared and the ants were all 
 at home. 
 
 ADDITIONAL FIELD EXPERIMENTS WITH REPELLENTS, 1908 
 
 After the failure of 1907 the experiments with repellents applied 
 to the seed were repeated in 1908 on a much larger scale, in the hope 
 of a more favorable season. The spring proved, however, to be similar 
 to that of the preceding year, and the results were not materially dif- 
 ferent. 
 
 In a field of twenty-five acres near Galesburg, the use of which 
 for our purpose was secured by contract with the owners, eight plots 
 each twenty corn rows wide and eighty rods in length were planted 
 on the 23d and 25th of May with seed treated with pure kerosene, 
 kerosene emulsion, scalecide, oil of lemon, carbolic acid, and formalin, 
 two plots of twenty rows each being planted at the same time with un- 
 treated seed as checks. These materials were used in the following 
 proportions: kerosene, 1 oz. to 4 gallons of seed; scalecide, oil of 
 lemon, carbolic acid, each in 10 per cent alcoholic solution of which 3 
 oz. were applied to a gallon of seed ; kerosene-soap emulsion contain- 
 ing 10 per cent of kerosene, also 3 oz. to the gallon; and formalin, 6 
 oz. of a 3 per cent solution to the gallon. The original infestation of 
 this field, ascertained by Mr. G. E. Sanders, April 22, was at the rate 
 of forty-three nests to the mile of furrow. 
 
 The weather of the spring at this place preceding the date of 
 
446 BULLETIN No. 178 [January, 
 
 planting is shown by the following extract from the field notes of Mr. 
 Sanders, the responsible assistant in charge of this work. 
 
 April 23, raining hard. 
 
 April 24, rained steadily almost all day. 
 
 April 27, raining more than half the time since 11 a. m. yester- 
 day ; now cold with some snow. Ground saturated before these rains. 
 
 May 1, showers today. 
 
 May 6, rainy on the 4th and 5th, the soil now too wet for plowing. 
 
 May 8, rained rather hard last night. 
 
 May 14, rained very hard late the preceding night, the ground 
 still too wet to work. 
 
 May 16, rained during the night. 
 
 May 25, hard rain during the night; too wet to plow on the fol- 
 lowing day. 
 
 May 28, rained during the night and all the morning. Also rained 
 on nights of 27th, 28th, and 29th, and rained very hard nights of June 
 6 and 7. 
 
 June 12, rained in the afternoon. 
 
 June 15, rains have prevented work in the fields since the 10th. 
 
 It will be noticed that the ground was planted on two days after 
 an interval of seven days since the last-mentioned rain, but that a hard 
 rain followed immediately after the planting was finished, and that 
 rain fell also on the second, third, and fourth days thereafter. 
 
 The effect of the treatment of this field was determined in five 
 different ways : (a) 500 hills were examined in each plot on each of 
 five dates between June 6 and July 10, and 1,000 hills in each plot 
 were examined June 1.6, record being made of the number of hills out 
 of each 500 found infested by ants ; (b) 10 hills infested by ants were 
 dug up in each plot, including, of course, the checks, on three dates 
 from June 17 to July 5, and the number of ants and root-lice found in 
 each of these hills was determined by counting; (c) the stalks and the 
 vacant hills in 500 hills of each plot were counted June 17; (d) at 
 husking time, in fall, the fertile and barren stalks in 1,000 hills of each 
 plot, and the ears borne by these hills, were counted, the ears being dis- 
 tinguished as small, medium, and large; and finally (e) the stalks and 
 ears in 2,000 hills of each plot were counted, and the yield of ears for 
 each 2,000 hills was weighed, 200 hills being taken for the purpose 
 from each of ten rows at the center of the 20-row strip. 
 
 As the last test was the most significant, its results are first given 
 in the following table. 
 
CORN ROOT-APHIS AND CONTROL OF ITS INJURIES 
 
 447 
 
 YIELD OF TWO THOUSAND HILLS FROM CENTRAL Rows OF EACH PLOT 
 OF EXPERIMENTAL FIELD, GALESBURG, 1908 
 
 Treatment of seed 
 
 Number 
 of stalks 
 
 Number 
 of ears 
 
 Weight of 
 corn in pounds 
 
 None (checks) 
 
 3,695 
 
 2,996 
 
 1,560 
 
 Kerosene 
 
 3,590 
 
 2,767 
 
 1,570 
 
 Carbolic acid 
 
 3,197 
 
 2,506 
 
 1,450 
 
 Scalecide 
 
 3399 
 
 2690 
 
 1,310 
 
 Kerosene emulsion 
 
 3,406 
 
 2,478 
 
 1,260 
 
 Oil of lemon 
 
 3,422 
 
 2,587 
 
 1,260 
 
 Formalin 
 
 2,039 
 
 1,931 
 
 1,230 
 
 From this it will be seen that the check plots and kerosene plot 
 had the highest yields, and that the other experimental plots, men- 
 tioned in the order of their yields, from highest to lowest, come as 
 follows : carbolic acid, scalecide, oil of lemon, kerosene emulsion, and 
 formalin. Two thousand hills of the kerosene plot yielded, indeed, 
 ten pounds more than the checks, but this difference is too slight to be 
 taken into account. In respect to the number of stalks in each 2,000 
 hills, the checks stand first, and the other plots come in the following 
 order: kerosene, oil of lemon, kerosene emulsion, scalecide, carbolic 
 acid, and formalin. The difference of 105 stalks between the kerosene 
 plot and the checks is only 3 per cent, and may probably be disre- 
 garded; but the difference of 498 stalks (13.5 per cent) between the 
 checks and the carbolic acid plot is too large to be ignored, while the 
 loss of 1,656 stalks in the formalin plot out of a possible 3,695 (45 per 
 cent) can only be explained as due to an original injury to the seed 
 a conclusion confirmed by reference to an earlier examination of the 
 number of stalks and missng hills in 500 hills of each plot, made June 
 1.7. At this time, while the checks averaged 931 stalks to this number 
 of hills, the formalin plot contained but 647, and while there were 41 
 missing hills in the checks there were 150 in the plot planted with 
 formalin. The loss in the number of ears (36 per cent) due to the 
 formalin treatment and in the total weight of the corn (21 per cent) 
 puts this conclusion beyond a doubt. The fact that the loss in number 
 of ears consequent upon a treatment of the seed with formalin was 
 less than the loss in the number of stalks, and that the loss in weight 
 of the total yield was still less than that in the number of ears, implies 
 that the formalin took the greatest effect upon the poorest kernels 
 which would have produced the weakest plants and the largest number 
 of barren stalks. 
 
 Something of the same tendency is shown in the results of the 
 
448 BULLETIN No. 178 [January, 
 
 carbolic acid experiment, where the loss in number of stalks was 13 
 per cent and that in weight of the yield was only 7 per cent. The 
 losses from the other experiments of this series were too small for 
 such analysis. 
 
 Our contract with the owner of this field provided that he should 
 be reimbursed for any net loss of yield attributable to our experiments, 
 and a comparison of the product of the experimental plots with that 
 of the checks showing a loss for the whole field of 60 bushels and 23 
 pounds of corn, a settlement was made with him on this basis. A tabu- 
 lation and analysis of the data from the earlier counts of hills, stalks, 
 ants' nests, ants, and aphids in the different plots simply confirm the 
 conclusion that no benefit was obtained from the treatment of the 
 seed-corn planted in this field in 1908. Parallel experiments carried 
 on in this, field and intended to test the effect of deep cultivation and 
 repeated harrowing and to show the consequences of a rotation from 
 corn to oats will be described later in connection with other experiments 
 of the same character. 
 
 USE OF REPELLENTS COMBINED WITH FERTILIZERS 
 
 The outcome of our repellent work of 1907 and 1908 evidently 
 called for a change of program. The amount of the repellent sub- 
 stances which could be held by the hard, slightly absorbent corn ker- 
 nel was so small that it was easily washed away by flooding rains and 
 yet was sufficient to injure much of the seed, if placed in contact with 
 it, whenever wet weather followed closely upon the planting. Either 
 the idea of protecting young corn for a time from ants and root-lice 
 by the use in the hill of substances offensive to the ants must be given 
 up, or some safer repellents or safer and more effective methods of 
 application must be found. As there is no possible advantage to the 
 seed itself to be derived from the application of repellents to it, the 
 corn kernels serving only as carriers of the repellent substances, it was 
 plain that some other carrier might be used to which the repellents 
 might be applied more freely and with less danger of injury to the 
 seed-corn or the plant; and as it was desirable that the use of this 
 carrier should be worth while in itself, a powdered fertilizer contain- 
 ing ingredients commonly needed on Illinois corn lands was selected 
 for the purpose. 
 
 Experiments were begun along this line in 1910, by W. P. Flint 
 and G. E. Sanders on the farm near Galesburg used in the field work 
 of 1908. In traveling twenty and two-thirds miles behind the plow 
 Flint and Sanders counted in the furrow 604 ants' nests of the corn- 
 
CORN ROOT-APHIS AND CONTROL OF ITS INJURIES 449 
 
 field ant, equivalent to 29.3 nests to the mile or 207 to the acre a case 
 of moderate infestation only. The substances selected for special trial 
 in this field were those which had been found most offensive to ants 
 in the laboratory experiments of Dr. Tanquary, already described in 
 this paper. Choice was finally made of tincture of asafetida and oil 
 of tansy, applied to bone meal to be dropped with the corn by an at- 
 tachment to the corn-planter known as a fertilizer-dropper. The bone 
 meal was used at the rate of 100 pounds per acre, and was treated 
 with the repellents as follows : Where oil of tansy was used, a quarter 
 of a pound of the oil was added to two quarts of alcohol and a quart 
 of water, the fluids being then well stirred into the hundred pounds 
 of the bone meal so as to mix the whole mass thoroly. The alcohol 
 soon evaporated, leaving the oil of tansy well distributed thru the 
 bone meal. The procedure with the tincture of asafetida was the same, 
 except that the bone meal was treated with two pints of this fluid 
 diluted with one and a half gallons of water. 
 
 Plots containing 3,520 to 5,060 hills each -that is 32 to 46 rows 
 wide and 11.0 hills long were planted May 12 with each of these sub- 
 stances, and similar plots were planted beside them, one with corn 
 accompanied by plain bone meal and the other with no addition to the 
 seed. 
 
 At husking time the yield of 1,800 hills taken from the twenty 
 central rows of each plot was separately weighed, with the result that 
 a considerable difference was shown in favor of the plots which had 
 received the repellent treatment. The untreated plot yielded at the 
 rate of 26.2 bushels; that of the bone meal plot, 26.6 bushels; 
 the bone-meal-asafetida plot, 31.8 bushels; and the oil of tansy plot, 
 37 bushels. The gain was practically nothing for the application of 
 plain bone meal, was 5.6 bushels for the use of asafetida, and 10.8 
 bushels for the use of oil of tansy. The cost of materials in these ex- 
 periments was $1.90 for the asafetida plot, and $2.95 for the oil of 
 tansy plot, the increase in the yield of the first being thus obtained at 
 34 cents a bushel, and that of the second at 27 cents. The general re- 
 sult of this experimental change in the method of applying repellents 
 at planting was the more encouraging because the gains above reported 
 were made during a year quite unfavorable to corn owing to the very 
 poor stand obtained. Cool weather after planting delayed germina- 
 tion and gave moles, mice, gophers, and insects an unusual opportunity 
 to devour the seed before it had started to grow. However, as it was 
 impossible to separate the loss due in these unusual conditions from 
 that attributable to infestation by root-lice, no exact estimate of re- 
 
450 BULLETIN No. 178 [January, 
 
 duced cost per bushel of the increase can be made for an ordinary year. 
 
 There was nothing in the early inspections made to indicate any 
 loss or injury of plants by these applications, and this notwithstanding 
 the fact that the weather of the spring was on the whole decidedly 
 rainy. The checks were planted May 11, and the experimental plots 
 on the 12th. From a complete meteorological record kept from April 
 16 to July 2, by Mr. W. P. Flint, who had principal charge of these 
 experiments in the field, it appears that the rainfall of the last fifteen 
 days of April was an inch, and that of May, 4 5/16 inches. Two and 
 five-sixteenth inches of this May rain fell during the days of the 
 month preceding the planting of the corn 1^2 inches on the first, 1/16 
 of an inch on the second, 5/8 of an inch on the seventh, and 1/8 on 
 the tenth. The first rains to follow the plantings of May 11 and 12, 
 were 1/8 of an inch on the fifteenth and 3/16 of an inch on the six- 
 teenth. 
 
 The complete record of rainfall, in inches, for the period referred 
 to is as follows: 
 
 April 16, snow, not measured. May 16, 3/16 inch. 
 
 17, 9-16 inch. 19, 1/4 inch. 
 
 22, 1-16 inch. 21, 1/16 inch. 
 
 23, unmeasured snow. 22, 1/4 inch. 
 
 24, unmeasured snow. 23, trace. 
 26, 1/4 inch. 25, trace. 
 
 30, 1/8 inch. 28, 1. 1/8 inch. 
 
 May 1, 1 1/2 inch. June 4, 1/8 inch. 
 
 2, 1/16 inch. 8, 1/4 inch. 
 
 7, 5/8 inch. 18, 1/8 inch. 
 
 10, 1/8 inch. 27, 3/4 inch. 
 
 15, 1/8 inch. 
 
 The temperature of ten days before the planting period averaged 
 78.6 degrees F. as a maximum, 41.3 degrees as a minimum, and 59.95 
 degrees as the mean. Those for ten days after the planting of the 
 plots were : maximum, 83.6 ; minimum, 48.2 ; and mean, 65.9. The 
 maximum reading of the first period was 92 degrees, and the minimum 
 was 29. For the second period the maximum was 97 degrees, and the 
 minimum, 29. With a rainfall of 1.7 inches for the first of these ten- 
 day periods and a mean temperature, in the sun, of 60 degrees ; and a 
 rainfall of .94 of an inch for the second period and a mean sunshine 
 temperature of 66 degrees, the weather of this planting-time may 
 properly be described as cool and wet. The following is a complete 
 record of temperatures from April 16 to July 2, as registered by a 
 
/9/5J CORN ROOT-APHIS AND CONTROL OF ITS INJURIES 443 
 
 others were just outside on the edge of the nest, and the remainder on 
 one corner of the base. Most of the larvae had been carried out, al- 
 tho a number between an eighth and a fourth of an inch from the 
 tar had been left. (Fig. 16.) There was no return of the ants to this 
 nest up to March 11, 6 days after the experiment was started. During 
 all this period the colony stayed together on a distant corner of the 
 base, so closely packed that a number were crowded off into the sur- 
 rounding water every day and drowned. When the experiment closed, 
 March 11, only about sixty ants were alive. 
 
 Experiment 5790, Vaporite. March 5, at 11:30, a bit of moist 
 vaporite at the center of a nest disturbed the ants but did not repel 
 them violently. They were mostly outside the nest together with their 
 larvae when this was established, and by 3:15 only half a dozen ants 
 had gone under the cover. The rest remained outside until 10 : 45 the 
 following day, when about twenty were seen at one corner of the nest 
 two and a quarter inches from the repellent. By 4:15 of that after- 
 noon (28 hours, 45 minutes), there were about fifty ants in the nest, 
 the nearest one and a half inches from the vaporite, but all the larvae 
 were still outside on the base. The ants now gradually returned, bring- 
 ing their larvae with them, until at 9 a. m. of March 7 they were all 
 in the nest. The repellent was not removed until 8 : 45, March 11, nearly 
 six days after the experiment was begun. At this time the ants nearest 
 the vaporite were three-eighths of an inch away. 
 
 Experiment 5791, Vermicide. April 14, at 8:15 a. m., sand 
 soaked with vermicide and tested on a fresh colony, which had been in 
 the cage for five days only from the field, drove them out in less than 
 a minute, many of their larvae being left behind together with five of 
 the workers which had touched the vermicide and had then died. In 
 fifteen minutes the ants were beginning to carry their larvae out from 
 under the cover, and piling them along the border of the nest, as 
 shown in the following sketch (Fig. 17). By 3 p. m. there was 
 nothing in the nest except some deserted larvae (Fig. 18), and these 
 conditions remained unchanged until two days had elapsed, when at 
 8 : 50 a. m. April 16, a 4 X 4 cover was substituted for the smaller one. 
 The ants paid no attention to this change, and the next day at 8 : 20 
 a. m. a still larger orange cover 5X6 inches was put in place. This 
 brought certain of the ants under its protection at one corner, and 
 others moved under slowly until at 9 : 30 about one-third of the colony 
 were in the nest, the nearest two and a fourth inches from the repel- 
 lent. This condition remained practically unchanged until 1 1 : 25 April 
 19 (5 days, 3 hours), when the small orange cover with which the ex- 
 
460 BULLETIN No. 178 [January, 
 
 size, planted at the same time, having been plowed as a check to a 
 depth of four inches and harrowed once without disking. The yield 
 of the latter was at the rate of 26.4 bushels per acre, and of the former 
 at the rate of 33.15 bushels per acre, a gain of 6^4 bushels, or nearly 
 25 per cent. The cost of these three diskings and one rolling was esti- 
 mated at $1.50 per acre, making the cost of the increased yield 22 
 cents a bushel. As there was a poor stand, owing to the character 
 of the spring weather, the cost of the increased yield would have been 
 measurably less per bushel if a fair stand and start had been secured 
 in the beginning. 
 
 In another experiment made at this same time and place the com- 
 parative values of one, two, and three diskings were brought into com- 
 parison, the treatment of the plots used being otherwise identical. For 
 this purpose three plots, each a hundred and sixty corn-rows long by 
 thirty-three rows wide, nearly an acre and a half in area and contain- 
 ing 5,280 hills, were specially plowed June 2. This ground had been 
 used earlier for an experiment with fall plowing and disking as com- 
 pared with the same treatment in spring; and the tract was now di- 
 vided, to insure an equal character and condition, into plots at right 
 angles to the earlier ones. One of these, Plot 9 of the year's series in 
 the Galesburg field, was plowed six inches deep June 2, disked three 
 times, June 3, 4, and 6, with a 20-inch disk to a depth of five inches, 
 leveled with a toothed harrow June 6, rolled June 7, lightly harrowed 
 to a depth of two inches the same day, planted, and finally rolled after 
 planting. Plot 10 was treated in like manner except that it was disked 
 but twice, and Plot 11 differed only in the fact that it was disked but 
 once. Eighty-five per cent of the ants' nests in these plots were com- 
 pletely turned out by the six-inch plowing and the other 15 per cent 
 were split by the plow, a part of each nest being left undisturbed in 
 the bottom of the furrow. Fifty nests were marked in each plot as it 
 was plowed, so that they could be identified later when the field was 
 disked. 
 
 At the first disking 45 per cent of these 150 nests, containing an 
 average of 21 ants and 2 larvae each, were found inhabited, the re- 
 maining 55 per cent of the ant colonies having already disappeared. 
 This observation indicates the effect of the plowing merely in dis- 
 persing the ants and breaking up their nests. Of the hundred marked 
 nests in plots 9 and 10, 30 per cent were still inhabited at the second 
 disking, with an average of 12 ants and no larvae in each, 70 per cent 
 of the colonies being now broken up by the plowing and a single disking. 
 
 The three plots of this June planting encountered much better 
 weather than those of the regular planting in early May, and the stand 
 
/9/5] CORN ROOT-APHIS AND CONTROL OF ITS INJURIES 461 
 
 was good while that of the May plantings was very poor. At husking 
 time the yield of 1,800 hills taken from the twenty central rows of each 
 plot was separately weighed, with the result that the several plots 
 showed yields per acre as follows: Plot 9 (thrice disked), 59.75 
 bushels; Plot 1.0 (twice disked), 60.73 bushels; Plot 11 (once disked), 
 64.7 bushels. In other words, the additional diskings beyond the first, 
 seemed to reduce the yield by 6.1 per cent for one additional disking, 
 and by 7.7 per cent for two additional diskings. It would seem that 
 under the circumstances of this experiment, some agricultural disad- 
 vantage followed the additional diskings which more than counter- 
 balanced the advantages due to a repeated breaking up of the nests of 
 the ants. Unfortunately no fair check plot was made for contrast 
 with the three plots used in this experiment. It was assumed at the 
 time that the checks of the original May planting would serve for this 
 planting also a supposition disappointed by the great difference in 
 the weather of the two periods. 
 
 EFFECT OF FALL PLOWING COMPARED WITH THAT OF 
 SPRING PLOWING 
 
 For the purpose of determining whether fall plowing and disk- 
 ing of an infested field was to be preferred to spring treatment, three 
 plots, Nos. 1, 2, and 3, in this Galesburg field, were plowed in the fall 
 of 1909, No. 3 to a depth of four inches only, and the others six 
 inches deep. Plot 3, plowed October 29 and 30, received no further 
 treatment in the fall; but it was necessary to disk it once in spring in 
 order to loosen up the plowed ground, and afterwards to harrow it 
 before planting. Plot 2 was plowed October 29, and disked three times 
 in succession in fall, and disked once in spring and harrowed also as 
 an immediate preparation for the planting of the corn. Plot 1 was 
 disked three times in fall, and rolled immediately after each disking, 
 and it was also disked twice in spring. Plot 6, a spring-plowed check 
 upon these fall-plowed plots, was broken up four inches deep May 4, 
 and harrowed once before planting. All these plots were planted on 
 the l.lth of May. Plots 1, 2, and 3 were kept until the first of June, 
 when the ground they occupied was plowed and replanted for an- 
 other experiment, already described, as plots 9, 10, and 11. 
 
 In the meantime a row of 90 hills of corn was dug from the cen- 
 tral part of each of these four plots on each of five different dates, 
 May 23, 25, 28, 30, and June 1, amounting to 450 hills for each plot; 
 and the usual counts were made each time of the number of hills in- 
 fested with ants, the total number of ants and aphids respectively, 
 
462 
 
 BULLETIN No. 178 
 
 [January. 
 
 and the total number of these insects found in each row. The follow- 
 ing table gives the totals of all these counts. 
 
 INFESTATION OF PLOTS PLOWED IN FALL AND IN SPRING 
 
 No. of 
 plot 
 
 Hills with 
 ants 
 
 Hills with 
 aphids 
 
 Total No. 
 of ants 
 
 Total No. 
 of aphids 
 
 
 1 
 2 
 3 
 6 
 
 SO 
 55 
 41 
 116 
 
 31 
 31 
 20 
 82 
 
 1,125 
 1,395 
 1,215 
 4,150 
 
 348 
 310 
 295 
 1,419 
 
 Fall plowing 
 Fall plowing 
 Fall plowing 
 Spring plowing 
 
 Plots 3 and 6 differ only in the fact that 3 was fall-plowed and 
 disked once in spring, while 6 was spring-plowed and not disked at all. 
 
 From a comparison of the data of these plots it appears that the 
 fall plowing and single spring-disking of 3 had a decided effect to 
 reduce the ant and root-louse infestation, this being only about a fourth 
 to a third as great in Plot 3 as it was in 6. On the other hand, a com- 
 parison of the data for plots 1, 2, and 3 shows practically no increased 
 advantage due to the more thorogoing treatment of plots 1 and 2 
 as compared with 3. 
 
 ROTATION OF CROPS WITH FALL PLOWING 
 
 Advantage was taken by Mr. Sanders at Galesburg in 1908 of the 
 fact that there lay immediately beside the field used in our experi- 
 ments another field which was to be planted to corn, but which had 
 been in oats in 1907. For the four years before this it had been in corn 
 continuously, while the experimental field had all been in corn without 
 interruption since 1904, and a part of it since 1903. 
 
 An experimental plot planted on this oats stubble, and treated like 
 our checks and our other experiments, would thus give us a means of 
 judging of the effect upon root-aphis infestation of a change for one 
 year from corn to oats. Such a comparison was complicated in this 
 case, however, by the fact that the oats field had been all plowed in 
 the fall of 1907, while the experimental field was not plowed until the 
 spring of 1908. What was actually got by planting a plot in the oats 
 field was consequently a chance to observe the apparent effect of rota- 
 tion and fall plowing combined. 
 
 This plot, like the others beside it, was 20 rows wide and 200 hills 
 long, thus containing 4,000 hills. In the fall of 1907 it was merely 
 plowed, to a depth not stated, and on the 19th of the following May it 
 was disked and harrowed. The two check plots in the experimental 
 
CORN ROOT-APHIS AND CONTROL OF ITS INJURIES 
 
 463 
 
 field, each likewise containing 2,000 hills, were plowed in May to a 
 depth of five inches, and, like the stubble plot, were disked once and 
 harrowed. Another experimental plot of the same size, known as the 
 cultivation plot, was plowed May 12 to a depth of seven inches, 
 disked three times, on the 15th, 19th, and 22d of May, the disk work- 
 ing the last time to a depth of four to four and a half inches, and har- 
 rowed. All these plots were planted on the 22d and 23d of May. The 
 following table gives Mr. Sanders's data of yield obtained November 
 15, when the crop from these plots was harvested. 
 
 COMPARATIVE YIELD OF CORN IN CHECK PLOTS, CULTIVA- 
 TION PLOT, AND AFTER OATS, 2,000 HlLLS 
 
 EACH, GALESBURG, 1908 
 
 Plots 
 
 Stalks 
 
 Ears 
 
 Weight 
 
 Check 
 
 3,712 
 3,679 
 
 2,929 
 3,064 
 
 1,505 
 1,625 
 
 Average 
 Cultivation 
 Oats 
 
 3,695 
 3,794 
 3,905 
 
 2,996 
 3,074 
 3,528 
 
 1,565 
 1.720 
 1,950 
 
 Compared with the average yield of the checks, the plot in the 
 fall-plowed oats stubble bore nearly 6 per cent more stalks than the 
 checks, 18 per cent more ears, and 25 per cent more corn by weight. 
 Compared with the cultivation plot, the differences in favor of the stub- 
 ble plot were nearly 3 per cent in the number of stalks, more than 1.1 
 per cent in the number of ears, and more than 13 per cent in the 
 weight of the crop. 
 
 There are several unknown elements capable of affecting this 
 comparison, for we know nothing of possible differences between the 
 oats and corn fields in respect to their fertility and other conditions due 
 to their previous cropping and treatment, and we are also ignorant of the 
 possible influence of differences in the weather at the times when the 
 plowing was done in fall and in spring. There is additional evidence, 
 however, that the advantage of the stubble plot was due, at least in part, 
 to the smaller number of root-lice harbored by it early in the season. 
 Twenty infested hills were dug from each of these plots and all the ants 
 and aphids contained in them were counted on the 9th of June, and again 
 on the 15th of that month, and similar counts were made from ten in- 
 fested hills dug up in each plot June 23 and July 5. 
 
464 
 
 BULLETIN No. 178 
 
 [January, 
 
 TOTAL COUNTS OF ANTS AND APHIDS, GALESBURG, JUNE AND JULY, 1908 
 
 Plots 
 
 Insects 
 
 June 9(20) 
 
 June 15(20) 
 
 June 23 (10) 
 
 Julys (10) 
 
 Checks 
 
 Ants 
 Aphids 
 Ants 
 Aphids 
 Ants 
 Aphids 
 
 583 
 564 
 588 
 
 153 
 15 
 159 
 
 861 
 819 
 1,057 
 
 551 
 48 
 529 
 
 455 
 877 
 775 
 
 397 
 67 
 378 
 
 695 
 635 
 
 615 
 
 638 
 605 
 335 
 
 Oats 
 
 Cultivation 
 
 
 From the above tabulation of the totals for these dates, it will 
 be seen that while the oats plot contained about as many ants as any 
 of the others, it contained only about a tenth of the number of root- 
 lice found in the other plots at the first three counts ; and these were 
 no doubt migrants from the other plots or the descendants of such 
 migrants. That it should have been so invaded by root-lice from ad- 
 jacent plots by the 5th of July, over forty days after planting, that 
 the infestation was now virtually equalized, is consistent with what 
 we have found in similar cases, and it illustrates forcibly the fact that 
 no field of corn is safe against this insect, even tho it may start 
 free from the root-lice in spring, as long as adjacent fields are in- 
 fested by it. Nevertheless, the larger yield of the oat-ground plot 
 than that of the cultivation plot indicates, as we should anticipate, that 
 rotation to oats makes in the end a more effective clearance of a field 
 than a deep spring preparation of the soil. 
 
 The fact must not be overlooked, however, that rotation to small 
 grains acts slowly in spring, giving the ant-aphis inhabitants of the 
 field sufficient food for some time, and ample opportunity to move, on 
 foot and on the wing, to other fields, while deep and thoro stirring 
 produces its effect at once, before the planting-time of the corn, killing 
 and keeping down the food plants of the aphids, and so dispersing 
 and disarranging the insect colonies as greatly to reduce the numbers 
 of the root-lice. 
 
 SUMMARY 
 
 1. The principal measures of protection against the corn root- 
 aphis are rotation of crops ; an early and deep plowing, followed by 
 the repeated deep disking, of corn ground heavily infested by ants or 
 known to have borne a crop injured by the root-aphis ; and the use of 
 repellent substances at planting-time, not by direct application to the 
 seed, (which is dangerous to germination and early growth,) but by 
 previous mixture with chemical fertilizers or other powdered sub- 
 stances, to be dropped with the seed by means of a fertilizer-dropper 
 attached to the corn-planter. Pages 405-408. 
 
I 9 I 5] CORN ROOT-APHIS AND CONTROL OF ITS INJURIES 465 
 
 2. Articles already published in the Twenty-fourth and Twenty- 
 fifth reports of the State Entomologist's office show marked benefit in 
 field experiments with deep plowing and repeated deep disking, and 
 also as a consequence of the treatment of seed-corn with oil of lemon 
 previous to planting, the last statement being based upon a single field 
 experiment made in 1906. Pages 408-410. 
 
 3. List of operations described in this paper. Pages 410 and 411. 
 
 4. Experiments of 1907 show that wet weather at planting-time 
 may either result in serious injury to the seed if repellents have been 
 applied to it direct, or in such washing away of the repellent sub- 
 stances that they produce no effect either on the seed or on the ants 
 and aphids, the character of the effect apparently depending on the 
 amount of rainfall and on its relation to the time of actual planting. 
 Comparative experiments show that the injurious effects reported 
 were not due, as at first surmised, to differences in the quality of the 
 repellents used in different operations. Pages 411-425. 
 
 5. Laboratory experiments with a considerable variety of repel- 
 lents applied by uniform methods to colonies of the corn-field ant in 
 a special cage, showed that oil of tansy, oil of lemon, anise oil, tincture 
 of asafetida, apterite, and vermicide were very strongly repellent, that 
 kerosene, camphor, and coal-tar were less effective repellents, and that 
 a considerable number of other substances tested were, if repellent at 
 all, too slightly so to make them practically useful. Pages 425_44;>. 
 
 6. Additional field experiments made in 1908, in a spring season 
 which proved to be very wet, resulted in no injury to the seed, and on 
 the other hand in no benefit to the crop, flooding rains apparently 
 washing away the repellents before they could take effect upon either 
 the seed-corn or the insects. Pages 445_448 
 
 7. Experiments made in 1910 with tincture of asafetida and oil 
 of lemon, applied first to bone meal which was then dropped with the 
 corn by means of a fertilizer-dropper attachment to the planter, and 
 tested by the yield at corn-husking, showed a gain of 5.6 bushels per 
 acre by the use of asafetida, and 10.8 bushels per acre by the use of 
 oil of tansy, the first gain being obtained at a cost for materials and 
 additional labor of thirty-four cents a bushel, and the second gain at 
 twenty-seven cents a bushel. This result was the more encouraging 
 since a very unfavorable spring caused an unusually poor stand and 
 reduced greatly the general yield of corn. In a good corn season the 
 gain would have been greater for the same cost. Pages 448-452. 
 
 8. Additional experiments with deep plowing and repeated disk- 
 ing made in 1909 showed, in one case, a decrease, due to the treatment, 
 of 43 per cent in the number of hills infested by ants, and 18 per cent 
 
466 BULLETIN No. 178 [January, 
 
 in the number of ants in the infested hills, and a decrease of 27 per 
 cent in the number of hills infested by root-lice and of 9 per cent in 
 the number of the root-lice themselves. In another case the number 
 of hills infested by ants was reduced 71 per cent and the number of 
 ants in the infested hills 83 per cent, the number of hills infested by 
 root-lice 86 per cent and the number of root-lice in the infested hills 
 61 per cent. The same experiment showed that deep disking with a 
 20-inch disk was much more effective in diminishing the number of 
 ants and root-lice than was the comparatively shallow disking of a 
 16-inch disk, the difference between the two methods of treatment 
 being 34 per cent and 48 per cent in the number of hills infested by 
 ants and by aphids respectively, and 1.3 per cent and 35 per cent in the 
 number of these insects themselves. It was incidentally shown by 
 this experiment that plowing to a depth of four inches does not suf- 
 ficiently break up the nests of the ants, but that about 85 per cent of 
 them may be broken up by plowing six inches deep, the remainder 
 being at least broken into. Pages 452_457. 
 
 9. Observations made at night upon the movements of colonies 
 of ants out of plots treated as above, and across furrows surrounding 
 them, showed nearly two and a half times as many migrations from 
 the plots deeply stirred as from the check plot. Migration lines across 
 furrows plowed thru the center of each of the plots a week after 
 planting, showed the amount of normal underground movements of 
 the ants at this time. Making due allowance for this, it appears that 
 the migration movement caused by the disturbance of the ants in 
 treated plots was more than five times as great as this normal. 
 
 Pages 457-459. 
 
 10. Plowing to a depth of six inches in a Galesburg field, in 1910. 
 dispersed 55 per cent of the ant colonies in this field, and one disking 
 after plowing dispersed 15 per cent more. Plowing six inches deep, 
 disking three times, and rolling once, increased the yield of the plot 
 nearly 25 per cent, at a cost of 22 cents a bushel. One 20-inch disk- 
 ing followed by rolling gave all the advantages obtainable by addi- 
 tional diskings. Pages 459-461. 
 
 11. Fall plowing and one spring disking are much more effective 
 than spring plowing with no disking, the latter containing about three 
 times as many ants and four times as many aphids as the former. 
 
 Pages 461 and 462 
 
 12. Change of corn ground to oats for one year, and fall-plowing 
 of the oats stubble, gave a larger yield by 25 per cent than adjacent 
 ground kept continuously in corn, this difference being accompanied 
 by a root-louse infestation of young corn on the oats stubble about 
 one-tenth that found in corn on old corn ground. Pages 462_464. 
 
UNIVERSITY OF ILLINOIS-URBANA 
 
 Q.630.7IL6B C001 
 
 BULLETIN. URBANA 
 166-181 1914-15 
 
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